Windows 2000 logon problem

I have a windows 2000 professional machine and it boots up and shows the “Press ctrl-alt-del to logon” screen just like normal. I enter the credentials and press ok. The pc looks like it want to bring up the desktop but then goes right back to the ctrl-alt-del logon screen!!!

I have tried logging on a a normal user, domain admin, workstation admin etc… and the same thing happens. HELP!!

Thanks