WinXP Pro keeps shutting down...

... I have been fighting spyware and viruses the past several weeks and have installed several antispyware programs. I also learned that I only had SP1 installed in the windows updates so I attempted to install SP2 EULA but each time I try to run it.. the system shuts down and reboots the computer. Now, the computer is shutting down and rebooting when I try to run other programs or use the Internet. I just switched from IE to Mozilla Firefox this morning in hopes this will provide a more stable internet browser. Although I am still fighting some nasty popups and spyware issues... my main concern is to stabalize the OS! I am a former MCP and have a strong background with MS products but its been a couple years since I worked in the field. Can someone please advise as to what I should do next?

Tee

 

Nuke the site from orbit. It's the only way to be sure.