Comment 129 for bug 226279

Hey pfeels, you want to download and burn a copy of the ubuntu alternate cd from here: http://www.ubuntu.com/getubuntu/download

Make sure the check the box under the green start download button to get the alternate disc.
(For futre reference, keep this disc handy as it's the only version of Ubuntu that has all the repare tools you need in one place)

Once you have downloaded and burned the .iso boot from the disk and select the "repair broken system" option. Once in that list select the option to reinstall Grub and all the kernal modules (this will revert your system back to the -16 kernel. You may just be able to reinstall Grub and be fine, so try that first.

Now you should be able to just reboot your system and all should be good. Keep this disc around and always burn the new version of this disc with each ubuntu flavor ubgrade. It's insanly handy for stuff like kernel tweaking (ie what you just did ;-)) and changing xorg.conf files, stuff that can bork your system to the point were it won't even boot anymore.

Hope that helps.