I had Ubuntu 9.04 working with nvidia display drivers, then I upgraded Ubuntu to 9.10. It boots to the desktop, the desktop looks great for a moment and then I get a screenful of pink and blue noise. How can I fix this? I've read that I should be able to drop out of the GUI with Ctrl-Alt-F1, but that doesn't work.
I got the help of a friend and here's what he ended up doing: Booted into recovery shell. Edited /etc/X11/xorg.conf and changed "nvidia" to "vesa". This allowed us to run the desktop GUI without getting the problem. He then went to the list of available display drivers under the "hardware drivers" menu and we selected a previous version of the nvidia proprietary drivers (just previous to the latest). The package manager downloaded and installed these drivers. We then changed "vesa" back to "nvidia" in xorg.conf, rebooted, and everything was good. The reason I couldn't drop out to a shell from the start was that the video problem seemed to kill the keyboard too. We also tried connecting an external monitor per DigitalRoss, but we never got anything to display. So the bottom line is that I'm not on the latest nvidia drivers, but at least I didn't have to downgrade anything else.
Go to System > Administration > Hardware drivers
Then activate the recommended drivers. If you've already done that, it most likely is a bug. There have been a lot of reported bugs in 9.10
The problem you are having is not precisely with Ubuntu, except in the sense that they take some responsibility for setting up Xorg and for including drivers for the text-based consoles.
What you really need to do is find an
/etc/X11/xorg.conf that works. On a cast-off Inspiron 8000, notorious for not running Linux (unless you have never-"up"graded firmware) I managed to get Ubuntu 9.04 working after some pain. I ultimately found out that the issue was that the Dell firmware was providing bogus data on frequency ranges and so xorg was rejecting all the workable modelines.
I was able to make the system usable for debugging by plugging in an external LCD to the VGA port. Another way would be to boot up into text console mode rather than X, which I believe can be done by having GRUB boot into "recovery mode". (I didn't have to try that due to the external monitor.)
Fixing your Xorg Xserver is going to be painful and it deserves a separate SO question so I don't have to answer it. At least if you can get going in console mode you have a chance. The kernel's console driver is considerably less ambitious and less prone to failure than the Xserver driver.
(And I should add a note: it looks like I have blamed Xorg, but really the problem is the secrecy surrounding the video chips. Because they are afraid of patent wars, they publish no interface info. It's really a pity they don't make an exception for the tiny part of the chip that does the 2D stuff, and it's unfortunate that the patent court and other influences have made the USA such a legal minefield.)