Unable to Boot Ubuntu 12.04 without USB support

By USB i mean USB flash drive of 4GB

Hi ,
you propably have right when you say

" I think grub is not copied on hdd and its there on my usb pen drive itself."

So boot with usb plugged and login to Ubuntu , then run these commands on terminal ..

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sudo add-apt-repository ppa:yannubuntu/boot-repair && sudo apt-get update
sudo apt-get install -y boot-repair && boot-repair
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Press Enter after each command.
Above commands will install an automatic repair tool for grub.
You must select [Recommended] repair .
Leave the program to do the job for you.
Reboot and see if problem solved.
Thanks

I tried what you suggested but it didn't work. Pasting the consoles output
sony@sony-Aspire-4720Z:~$ sudo add-apt-repository ppa:yannubuntu/boot-repair
You are about to add the following PPA to your system:
 Simple tool to repair frequent boot problems.

Website: https://launchpad.net/boot-repair
 More info: https://launchpad.net/~yannubuntu/+archive/boot-repair
Press [ENTER] to continue or ctrl-c to cancel adding it

Executing: gpg --ignore-time-conflict --no-options --no-default-keyring --secret-keyring /tmp/tmp.Kc1rE4oIun --trustdb-name /etc/apt/trustdb.gpg --keyring /etc/apt/trusted.gpg --primary-keyring /etc/apt/trusted.gpg --keyserver hkp://keyserver.ubuntu.com:80/ --recv 3C48D16124B50277AF10D27F32B18A1260D8DA0B
gpg: requesting key 60D8DA0B from hkp server keyserver.ubuntu.com
gpg: key 60D8DA0B: "Launchpad PPA for YannUbuntu" not changed
gpg: Total number processed: 1
gpg: unchanged: 1
sony@sony-Aspire-4720Z:~$ sudo apt-get update
E: Could not get lock /var/lib/apt/lists/lock - open (11: Resource temporarily unavailable)
E: Unable to lock directory /var/lib/apt/lists/

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I have only one os in my laptop, no windows nothing. When have installed ubuntu from cd, it works fine, but I am not able to boot it without usb flash drive. Once it is booted, i am able to work without it. What is missing ?
You help would be appreciated.

http://ubuntuforums.org/showthread.php?t=1986795

My problem statement is some thing indicated in the link above

Hi ,
you don't miss something . Probably the grub bootloader installed in Usb stick and not on /dev/sda.

You need to reinstall it.
Boot-repair do this job (re-installation) automatically.

Is something wrong with your apt/lists.
So , apply below commands carefully (copy-paste from here to terminal)

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sudo rm /var/lib/apt/lists* -vf
sudo apt-get update
===================================
No other program must be open when you apply above commands (check if update manager icon is open , if yes then first close it)

Also ,when you run [Recommended] repair with boot-repair , you must have unplugged the Usb.
Thanks

I've tried to re-install GRUB after booting into my system, removing the stick, and running grub-install /dev/sda

It solved my problem :-)
Now, my system boots without usb flash drive support.