If you have positively elimated pests from the probable causes, you might start looking for faulty hardware or software. XP can be set to restart by default as a way to deal with a fatal error. You could have a weak power supply, a hot running processor, bad RAM, etc. You can try reseating components, cables and such and run with your case open with a fan blowing in to rule out a heat problem. If you find heat to be the culprit, I would clean the dust from fans and the processor heat sink. Check the wattage on your PS to be sure it's more than adequate for the job.
I'm not sure if anyone else has had this problem before or not but, my computer keeps restarting all by itself. It was doing this maybe once or twice a day for a while, then at times it was going 2-3 days without restarting before it did it again. This past Thursday, I downloaded Ad-Aware and found out I had a ton of browser hijacking programs on my computer. I quarantined them and deleted them, and all was fine. My computer was running better, and it wasn't restarting.
Last night, I saw a message pop up saying my virtual memory was low and I needed to increase the paging file. I set it to System Managed Size, and figured all was good to go. This afternoon, I was surfing around and my computer restarted itself again. At first I thought it was because my browser had been hijacked again, but a scan revealed it hadn't. Is it simply that I need more virtual memory, or is something else possibly wrong with my system?
I'm using a Compaq Presario 5300US, with Windows XP Home Service Pack 2, 256MB RAM, 20GB Hard Drive.
Any help with this problem would be greatly appreciated.