Did you just do an upgrade in Ubuntu, and are now stuck with a 640x480 resolution ?
This seems like a common problem on machines with Nvidia based graphics cards. There are various solutions given on the net, but the one that works for me ... remove the Xorg.conf file.
Heres how you do it.
1. Start up your linux.
2. press the keys together : ctrl+alt+F1 . This will bring you to the command prompt.
3. Login with your username which has admin privilidges.
4. mv the Xorg.conf file to something . E.g. I used the following :
sudo mv /etc/X11/Xorg.conf /etc/X11/Xorg.bk
5. go back to the UI screen by pressing ctrl+alt+F7 .
6. press ctrl+alt+backspace to restart the X server.
presto , it will recreate the Xorg.conf file and you should be back to optimal resolution now.
If you run into issues, you can go back to the F1 screen, and mv the backup back to the original filename. And try your luck on google.