login problem with Ubuntu 10.4

[macbeth]

Afternoon folks,

I downloaded Ubuntu 10.4 the other night and installed it on a machine that
had 8.04 on it.

Everything looked just fine.  Rebooted, got to the login screen, logged in
and gnome came up.  After about a second, the screen flashed black and went
back to the login screen.

Try as I might, I can't get in.  I went into safe Gnome just fine, but I
have no idea what to look for.  Or, even what to google for.

Any thoughts, pointers, sites, suggestions, would be greatly appreciated.

thanks,
Michael