Virus Help Needed

I am experiencing great difficulty with my PC. I am running Windows XP Professional and my computer now gets to the log in screen and restarts itself. This has gotten progressively worse over the last couple of days. I can no longer log off the computer, it is continually restarting itself. The only way I can shut it off is manually. Any help would be greatly appreciated.

 

First please get Spybot S&D to clear out most of the spyware.

Short tutorial and download link here:
http://tomcoyote.org/SPYBOT/

Fix everything SpybotSD labels in red.

Then after reboot:
Download 'Hijack This!'. http://www.tomcoyote.org/hjt/
Unzip, doubleclick HijackThis.exe, and hit "Scan".

When the scan is finished, the "Scan" button will change into a "Save Log" button.
Press that, save the log, load it in Notepad, and copy its contents here. Most of what it lists will be harmless or even essential, don't fix anything yet.
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