System Reboots And Boots At Random

This is a very serious situation for me. I have XP/sp2/608ram. 11 days prior to the problem I upgraded from 128 + 512 ram as well as upgraded to a LG 16x Super Multi DVD/CD rewriter. Everything ran fine. Just noting. Thursday I bought and installed a wireless router. When booting down there was a hissing/crackling noise from the subwoofer, and consequently the subwoofer died. Saturday afternoon, while listening to winamp media stream, the system suddenly informed me that windows was logging off. It then at random intervals continuously rebooted. Only by turning off my surge protector was I able to stop it from happening. While trying to troubleshoot the problem I have determined that it usually occurs within 45min-1 1/2 hours after turning on the system ( except for a couple of instances where it stayed on for 5 1/2 hours and a different instance in which it started to boot down after 7 min.) I also while attempting to post this the first time booted down my machine to off mode. Several minutes past and the machine booted up again to begin the cycle of hell. I have Freedom anti-virus, which detects nothing. In closing, I'm desperate for some feedback as I am new to Montreal and don't know any shops that I know and can trust and so I am therefore reduced to take it to futureshop.