I had a problem like yours when I upgraded from 7.04 to 7.10. Tried everything I found on forums. Nothing worked. I installed and ran envy (
http://albertomilone.com/nvidia_scripts1.html) and it fixed the problem. Give it a try if you have not done so already.
For those who don't know what the problem is, mine went like this:
Upgraded from a perfectly working Kubuntu 7.04 to 7.10 on a Dell D620 and re-booted. The machine did not find any "screens" and dropped me into command line mode. I installed the nVidia driver and started X. Worked fine. Re-booted and no screens. Back to command line. And on, and on, and on! The non-nVidia driver worked fine, but I wanted all the functionality.