It would appear that a worm has badly infected my PC. I cannot access Internet Explorer and the computer shuts down after a few minutes of operation. I've tried to go through your initial steps listed but whenever I try and download anything, the system shuts down. I ran AdAware in safe mode and it identified "Win32.Worm.Zhelatin." as well as "Win32.trojanproxy.agent.dll" with a root of C:\WINDOWS\system32\rsvp32.2.dll. However AdAware could not remove the file.
I'm using Windows XP Pro and my firewall is Zone Alarm. When the computer is running, Zone Alarm pops up frequently with "Services and Controller app wants to accept connections from the internet" as well as "wldap32.dll is trying to access the internet" and "svchots.exe is trying to access the trusted zone."
I did not post a HiJack log as I was unable to complete your recommended 1st steps so I wasn't sure how to proceed. Any help is greatly appreciated.