I cant install anything after uninstallation of gnome 3

Hi please do this:
1. Open a terminal
2. Run this command:
cat /etc/apt/sources.list -n; sudo apt-get update

3. Copy and paste here all the terminal says.

Even if you get it sorted you will more than likely have an unstable desktop UI. Why did you install Gnome3 on a production system (ie. Not a test suite)? The pages showing how to do it CLEARLY state it will break your OS. If Gnome3 was suitable for Natty then it will more than likly have been updated. The differences in Gnome3 and Gnome2 are HUGE! The settings and such for your apps are all 100% geared around Gnome2 so changing it to something else will break stuff.

I'd just reinstall. If you want Gnome3 so very badly, just install Oneiric and you will have it. Gnome3 is default in Gnome Oneiric.

toshiba@toshiba-Satellite-L300:~$ cat /etc/apt/sources.list -n; sudo apt-get update
     1 # deb cdrom:[Ubuntu 11.04 _Natty Narwhal_ - Release i386 (20110427.1)]/ natty main restricted
     2
     3 # See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
     4 # newer versions of the distribution.
     5 deb http://in.archive.ubuntu.com/ubuntu/ natty main restricted
     6 deb-src http://in.archive.ubuntu.com/ubuntu/ natty main restricted
     7
     8 ## Major bug fix updates produced after the final release of the
     9 ## distribution.
    10 deb http://in.archive.ubuntu.com/ubuntu/ natty-updates main restricted
    11 deb-src http://in.archive.ubuntu.com/ubuntu/ natty-updates main restricted
    12
    13 ## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
    14 ## team. Also, please note that software in universe WILL NOT receive any
    15 ## review or updates from the Ubuntu security team.
    16 deb http://in.archive.ubuntu.com/ubuntu/ natty universe
    17 deb-src http://in.archive.ubuntu.com/ubuntu/ natty universe
    18 deb http://in.archive.ubuntu.com/ubuntu/ natty-updates universe
    19 deb-src http://in.archive.ubuntu.com/ubuntu/ natty-updates universe
    20
    21 ## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
    22 ## team, and may not be under a free licence. Please satisfy yourself as to
    23 ## your rights to use the software. Also, please note that software in
    24 ## multiverse WILL NOT receive any review or updates from the Ubuntu
    25 ## security team.
    26 deb http://in.archive.ubuntu.com/ubuntu/ natty multiverse
    27 deb-src http://in.archive.ubuntu.com/ubuntu/ natty multiverse
    28 deb http://in.archive.ubuntu.com/ubuntu/ natty-updates multiverse
    29 deb-src http://in.archive.ubuntu.com/ubuntu/ natty-updates multiverse
    30
    31 ## Uncomment the following two lines to add software from the 'backports'
    32 ## repository.
    33 ## N.B. software from this repository may not have been tested as
    34 ## extensively as that contained in the main release, although it includes
    35 ## newer versions of some applications which may provide useful features.
    36 ## Also, please note that software in backports WILL NOT receive any review
    37 ## or updates from the Ubuntu security team.
    38 # deb http://in.archive.ubuntu.com/ubuntu/ natty-backports main restricted universe multiverse
    39 # deb-src http://in.archive.ubuntu.com/ubuntu/ natty-backports main restricted universe multiverse
    40
    41 deb http://security.ubuntu.com/ubuntu natty-security main restricted
    42 deb-src http://security.ubuntu.com/ubuntu natty-security main restricted
    43 deb http://security.ubuntu.com/ubuntu natty-security universe
    44 deb-src http://security.ubuntu.com/ubuntu natty-security universe
    45 deb http://security.ubuntu.com/ubuntu natty-security multiverse
    46 deb-src http://security.ubuntu.com/ubuntu natty-security multiverse
    47
    48 ## Uncomment the following two lines to add software from Canonical's
    49 ## 'partner' repository.
    50 ## This software is not part of Ubuntu, but is offered by Canonical and the
    51 ## respective vendors as a service to Ubuntu users.
    52 deb http://archive.canonical.com/ubuntu natty partner
    53 # deb-src http://archive.canonical.com/ubuntu natty partner
    54
    55 ## This software is not part of Ubuntu, but is offered by third-party
    56 ## developers who want to ship their latest software.
    57 deb http://extras.ubuntu.com/ubuntu natty main
    58 deb-src http://extras.ubuntu.com/ubuntu natty main
    59 deb http://buc.billera.eu/ubuntu/ binary/
[sudo] password for toshiba:
Ign http://archive.canonical.com natty InRelease
Ign http://ppa.launchpad.net natty InRelease
Ign http://ppa.launchpad.net natty InRelease
Ign http://extras.ubuntu.com natty InRelease
Ign http://security.ubuntu.com natty-security InRelease
Ign http://in.archive.ubuntu.com natty InRelease
Ign http://in.archive.ubuntu.com natty-updates InRelease
Hit http://archive.canonical.com natty Release.gpg
Hit http://ppa.launchpad.net natty Release.gpg
Get:1 http://extras.ubuntu.com natty Release.gpg [72 B]
Get:2 http://security.ubuntu.com natty-security Release.gpg [198 B]
Hit http://in.archive.ubuntu.com natty Release.gpg
Hit http://archive.canonical.com natty Release
Hit http://extras.ubuntu.com natty Release
Get:3 http://ppa.launchpad.net natty Release.gpg [316 B]
Get:4 http://security.ubuntu.com natty-security Release [31.4 kB]
Get:5 http://in.archive.ubuntu.com natty-updates Release.gpg [198 B]
Hit http://ppa.launchpad.net natty Release
Ign http://buc.billera.eu binary/ InRelease
Hit http://in.archive.ubuntu.com natty Release
Hit http://archive.canonical.com natty/partner i386 Packages
Hit http://extras.ubuntu.com natty/main Sources
Get:6 http://ppa.launchpad.net natty Release [9,741 B]
Ign http://buc.billera.eu binary/ Release.gpg
Get:7 http://in.archive.ubuntu.com natty-updates Release [31.4 kB]
Ign http://archive.canonical.com natty/partner TranslationIndex
Hit http://extras.ubuntu.com natty/main i386 Packages
Ign http://extras.ubuntu.com natty/main TranslationIndex
Hit http://buc.billera.eu binary/ Release
Get:8 http://security.ubuntu.com natty-security/main Sources [67.5 kB]
Hit http://ppa.launchpad.net natty/main Sources
Hit http://ppa.launchpad.net natty/main i386 Packages
Ign http://ppa.launchpad.net natty/main TranslationIndex
Ign http://buc.billera.eu binary/ Packages/DiffIndex
Get:9 http://ppa.launchpad.net natty/main i386 Packages [574 B]
Ign http://ppa.launchpad.net natty/main TranslationIndex
Hit http://in.archive.ubuntu.com natty/main Sources
Hit http://in.archive.ubuntu.com natty/restricted Sources
Hit http://in.archive.ubuntu.com natty/universe Sources
Hit http://in.archive.ubuntu.com natty/multiverse Sources
Hit http://in.archive.ubuntu.com natty/main i386 Packages
Hit http://in.archive.ubuntu.com natty/restricted i386 Packages
Hit http://in.archive.ubuntu.com natty/universe i386 Packages
Hit http://in.archive.ubuntu.com natty/multiverse i386 Packages
Ign http://in.archive.ubuntu.com natty/main TranslationIndex
Ign http://in.archive.ubuntu.com natty/multiverse TranslationIndex
Ign http://in.archive.ubuntu.com natty/restricted TranslationIndex
Ign http://in.archive.ubuntu.com natty/universe TranslationIndex
Get:10 http://in.archive.ubuntu.com natty-updates/main Sources [105 kB]
Get:11 http://in.archive.ubuntu.com natty-updates/restricted Sources [14 B]
Get:12 http://in.archive.ubuntu.com natty-updates/universe Sources [25.9 kB]
Get:13 http://security.ubuntu.com natty-security/restricted Sources [14 B]
Get:14 http://security.ubuntu.com natty-security/universe Sources [11.3 kB]
Get:15 http://in.archive.ubuntu.com natty-updates/multiverse Sources [1,890 B]
Get:16 http://in.archive.ubuntu.com natty-updates/main i386 Packages [318 kB]
Get:17 http://security.ubuntu.com natty-security/multiverse Sources [650 B]
Get:18 http://security.ubuntu.com natty-security/main i386 Packages [179 kB]
Ign http://archive.canonical.com natty/partner Translation-ml_IN
Ign http://archive.canonical.com natty/partner Translation-ml
Ign http://archive.canonical.com natty/partner Translation-en_US
Ign http://archive.canonical.com natty/partner Translation-en
Ign http://extras.ubuntu.com natty/main Translation-ml_IN
Ign http://extras.ubuntu.com natty/main Translation-ml
Ign http://extras.ubuntu.com natty/main Translation-en_US
Ign http://extras.ubuntu.com natty/main Translation-en
Ign http://ppa.launchpad.net natty/main Translation-ml_IN
Ign http://ppa.launchpad.net natty/main Translation-ml
Ign http://ppa.launchpad.net natty/main Translation-en_US
Ign http://ppa.launchpad.net natty/main Translation-en
Ign http://ppa.launchpad.net natty/main Translation-ml_IN
Ign http://ppa.launchpad.net natty/main Translation-ml
Hit http://buc.billera.eu binary/ Packages
Ign http://ppa.launchpad.net natty/main Translation-en_US
Ign http://ppa.launchpad.net natty/main Translation-en
Ign http://buc.billera.eu binary/ Translation-ml_IN
Ign http://buc.billera.eu binary/ Translation-ml
Ign http://buc.billera.eu binary/ Translation-en_US
Ign http://buc.billera.eu binary/ Translation-en
Get:19 http://security.ubuntu.com natty-security/restricted i386 Packages [14 B]
Get:20 http://security.ubuntu.com natty-security/universe i386 Packages [38.4 kB]
Get:21 http://in.archive.ubuntu.com natty-updates/restricted i386 Packages [14 B]
Get:22 http://in.archive.ubuntu.com natty-updates/universe i386 Packages [93.1 kB]
Get:23 http://security.ubuntu.com natty-security/multiverse i386 Packages [2,071 B]
Ign http://security.ubuntu.com natty-security/main TranslationIndex
Ign http://security.ubuntu.com natty-security/multiverse TranslationIndex
Ign http://security.ubuntu.com natty-security/restricted TranslationIndex
Ign http://security.ubuntu.com natty-security/universe TranslationIndex
Get:24 http://in.archive.ubuntu.com natty-updates/multiverse i386 Packages [4,258 B]
Ign http://in.archive.ubuntu.com natty-updates/main TranslationIndex
Ign http://in.archive.ubuntu.com natty-updates/multiverse TranslationIndex
Ign http://in.archive.ubuntu.com natty-updates/restricted TranslationIndex
Ign http://in.archive.ubuntu.com natty-updates/universe TranslationIndex
Hit http://in.archive.ubuntu.com natty/main Translation-ml
Ign http://in.archive.ubuntu.com natty/main Translation-ml_IN
Ign http://in.archive.ubuntu.com natty/main Translation-en_US
Ign http://in.archive.ubuntu.com natty/main Translation-en
Ign http://in.archive.ubuntu.com natty/multiverse Translation-ml_IN
Ign http://in.archive.ubuntu.com natty/multiverse Translation-ml
Ign http://in.archive.ubuntu.com natty/multiverse Translation-en_US
Ign http://in.archive.ubuntu.com natty/multiverse Translation-en
Ign http://in.archive.ubuntu.com natty/restricted Translation-ml_IN
Ign http://in.archive.ubuntu.com natty/restricted Translation-ml
Ign http://in.archive.ubuntu.com natty/restricted Translation-en_US
Ign http://in.archive.ubuntu.com natty/restricted Translation-en
Ign http://in.archive.ubuntu.com natty/universe Translation-ml_IN
Ign http://in.archive.ubuntu.com natty/universe Translation-ml
Ign http://in.archive.ubuntu.com natty/universe Translation-en_US
Ign http://in.archive.ubuntu.com natty/universe Translation-en
Ign http://in.archive.ubuntu.com natty-updates/main Translation-ml_IN
Ign http://in.archive.ubuntu.com natty-updates/main Translation-ml
Ign http://in.archive.ubuntu.com natty-updates/main Translation-en_US
Ign http://in.archive.ubuntu.com natty-updates/main Translation-en
Ign http://in.archive.ubuntu.com natty-updates/multiverse Translation-ml_IN
Ign http://in.archive.ubuntu.com natty-updates/multiverse Translation-ml
Ign http://in.archive.ubuntu.com natty-updates/multiverse Translation-en_US
Ign http://in.archive.ubuntu.com natty-updates/multiverse Translation-en
Ign http://in.archive.ubuntu.com natty-updates/restricted Translation-ml_IN
Ign http://in.archive.ubuntu.com natty-updates/restricted Translation-ml
Ign http://in.archive.ubuntu.com natty-updates/restricted Translation-en_US
Ign http://in.archive.ubuntu.com natty-updates/restricted Translation-en
Ign http://in.archive.ubuntu.com natty-updates/universe Translation-ml_IN
Ign http://in.archive.ubuntu.com natty-updates/universe Translation-ml
Ign http://in.archive.ubuntu.com natty-updates/universe Translation-en_US
Ign http://in.archive.ubuntu.com natty-updates/universe Translation-en
Ign http://security.ubuntu.com natty-security/main Translation-ml_IN
Ign http://security.ubuntu.com natty-security/main Translation-ml
Ign http://security.ubuntu.com natty-security/main Translation-en_US
Ign http://security.ubuntu.com natty-security/main Translation-en
Ign http://security.ubuntu.com natty-security/multiverse Translation-ml_IN
Ign http://security.ubuntu.com natty-security/multiverse Translation-ml
Ign http://security.ubuntu.com natty-security/multiverse Translation-en_US
Ign http://security.ubuntu.com natty-security/multiverse Translation-en
Ign http://security.ubuntu.com natty-security/restricted Translation-ml_IN
Ign http://security.ubuntu.com natty-security/restricted Translation-ml
Ign http://security.ubuntu.com natty-security/restricted Translation-en_US
Ign http://security.ubuntu.com natty-security/restricted Translation-en
Ign http://security.ubuntu.com natty-security/universe Translation-ml_IN
Ign http://security.ubuntu.com natty-security/universe Translation-ml
Ign http://security.ubuntu.com natty-security/universe Translation-en_US
Ign http://security.ubuntu.com natty-security/universe Translation-en
Fetched 921 kB in 31s (29.6 kB/s)
Reading package lists... Done

So Gnome3 is unsupported in 11.04..............When i look in the gnome-look.org I saw better themes for gnome 3.x so i just tried it........@andrew-woodhead666: you meant 11.10 Oneiric Ocelot by saying Gnome Oneiric

Off the top of my head, try:

sudo apt-get upgrade -f
sudo dpkg-reconfigure -a

If that works:

sudo apt-get install ubuntu-desktop

@jeff sharpe I think it has worked now i can install other softwares but a dialougue box appears saying detected an error......with 2 options report problem and cancel.....!!!!!