I run Norton Internet Security 2007 as well as Norton System works basic.
I had some problems about a month ago and did a clean re-install of XP w/service pack2. When I installed the Norton and tried to do the first scan my PC shut down about half way through. I tried a couple of more times, including in safe mode, and had the same result. I contacted Norton tech support and after several hours and many tweaks they decided I had no malware and got it to do a scan, though not as complete a scan as it does normally. well, after a month I have a pared down scan and still shut down at random points. It does seem to be when the processor is under load, such as when I tried to run the AVG scan.
Any thoughts would be greatly appreciated.