I had the very same problem. It turns out that each time the kernel was upgraded on my machine, I chose to keep the current file rather than using the package maintainer's version. After manually editing /boot/grub/menu.lst to include the most-recent kernel, I rebooted and voila - the problem was fixed using the kernel 2.6.27-4-generic.
On a side note, prior to updating the grub list, I received the following error in xorg.conf (file is abbreviated) each time I ran sudo nvidia-xconfig: Section "Module" Load "type1" EndSection -- Upgrade to Ubuntu 8.10 Alpha 3 stops Nvidia driver working https://bugs.launchpad.net/bugs/252160 You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs