I've got a problem. I rebooted my system, and it has never re-booted fully. The last line on the screen is:

Starting GNOME Display Manager: gdm

it has been on that line, with the cursor blinking for about an hour now. I have no idea what to do. I've got KnoppMyth R5A16

UPDATE:
Okay -- I am able to get into the system using SSH from another computer -- but every command takes about 5 minutes to execute. The monitor on the frozen/slow system STILL remains on the line I noted above. Any suggestions?