Unable to access the internet after installing updates

If you run:

ping -c 4 8.8.8.8

Do you get replies?

The reply is "network unreachable". I tried using both wireless and wired connections.

Thank you for the help.

Probably Bug #1511735

Do you have the trusty-proposed repository enabled?

see also https://answers.launchpad.net/ubuntu/+question/284147

Using the suggestions in question 284147, I have determined that I do indeed have the bug. Using the "uname -a" command I got this result:

david@david-NE56R:~$ uname -a
Linux david-NE56R 3.8.0-34-generic #49~precise1-Ubuntu SMP Wed Nov 13 18:05:00 UTC 2013 x86_64 x86_64 x86_64 GNU/Linux
david@david-NE56R:~$

Again using the procedure suggested in answer #20 of that question, I downloaded the packages and attempted to force downgrade, and got this result in terminal:

david@david-laptop:~$ cd /media/david/UUI
david@david-laptop:/media/david/UUI$ sudo dpkg -i --force-downgrade libnl-3-200_3.2.21-1_amd64 .deb libnl-genl-3-200_3.2.21-1_amd64.deb libnl-route-3-200_3.2.21-1_amd64 .deb
[sudo] password for david:
dpkg: error processing archive libnl-3-200_3.2.21-1_amd64 (--install):
 cannot access archive: No such file or directory
dpkg: error processing archive .deb (--install):
 cannot access archive: No such file or directory
dpkg: warning: downgrading libnl-genl-3-200:amd64 from 3.2.21-1ubuntu1 to 3.2.21-1
(Reading database ... 1316269 files and directories currently installed.)
Preparing to unpack libnl-genl-3-200_3.2.21-1_amd64.deb ...
Unpacking libnl-genl-3-200:amd64 (3.2.21-1) over (3.2.21-1ubuntu1) ...
dpkg: error processing archive libnl-route-3-200_3.2.21-1_amd64 (--install):
 cannot access archive: No such file or directory
dpkg: error processing archive .deb (--install):
 cannot access archive: No such file or directory
dpkg: dependency problems prevent configuration of libnl-genl-3-200:amd64:
 libnl-genl-3-200:amd64 depends on libnl-3-200 (= 3.2.21-1); however:
  Version of libnl-3-200:amd64 on system is 3.2.21-1ubuntu1.

The files I downloaded are:
libnl-3-200_3.2.21-1_amd64.deb
libnl-genl-3-200_3.2.21-1_amd64.deb
libnl-route-3-200_3.2.21-1_amd64.deb

Any ideas as to what I have done wrong?

Again, thank you.

I have resolved my problem, at least in part. My boot menu has the option to boot a previous installation of Ubuntu, which in my case was 12.02LTS. That version was working fine so I upgraded it to 14.04.3 via a fresh download. It is working fine, and since I have been using sync (a great feature!) I was able to update all my favourites and such. The broken load is still broaken, but it is not the primary version right now.

I also took the precaution of turning off the trusty-proposed repository.

I still need to figure out what I am doing wrong on the force downgrade, but there is not so much urgency.

There was a typo error in the instructions (extra space characters), only corrected in a later comment.

Try again with

cd /media/david/UUI
sudo dpkg -i --force-downgrade libnl-3-200_3.2.21-1_amd64.deb libnl-genl-3-200_3.2.21-1_amd64.deb libnl-route-3-200_3.2.21-1_amd64.deb

That worked, thank you for your help, and for your patience.