Ubuntu hangs in startup after attempt at upgrade

I tried upgrading to 8.04, and now the machine won't boot at all, not even into single-user mode.

It runs startup scripts, but stops after printing:
Being: Running /scripts/init-bottom
Done.

I can bring the machine up from a LiveCD, and look at the disk that way, but I have no idea what I need to change in order to unwedge it. Any suggestions? I ran fsck (nothing wrong) and looked at the files in /var/log but couldn't see anything very suggestive.

Thanks for your help....