Comment 3 for bug 464591

I had this same problem. Using Nvidia 8800gts, previously working perfectly in 9.04.

After upgrade X was broken, booted to CLI with flickering. Once logged in, startx said no screens and xinit no such file or folder.

After editing xorg.conf using nano to make X use vesa driver instead, I managed to boot to a desktop.

However The first time I did this I got four popup warning messages on the desktop saying critical kernel failure.

In the end I had to do a fresh install.