Comment 15 for bug 568939

A solution to this issue is posted on Ubuntu forums.

See post titled "Stuck with black screen on booting after 10.04 upgrade" See comments #7, 8,9 and 10 especially. http://ubuntuforums.org/showthread.php?t=1467235

The solution people found is to boot into the older kernel, and then install a kernel that's even newer than the one that ships with the Lucid 10.04 iso. Seems everything works then.