I am using windwos xp pro with sp2 and norton internet security protection tool. but my pc shuts down within 10 seconds of starting without any valid reason and then it restarts itself. It does not shut down completely, but this cycle of starting and then restarting continues to no end. I did restart and turned it off many a time, but it still continues to shut itself as soon as it starts. Can any one help? There are no viruses or any thing else. The cpu temp in bios is also set to the maximum and I am not playing any games or doing temp intensive work at all. I have not changed any setting in bios recently. All I am doing is just normal surfing etc. Thanks.

if you have more than one stick of memory take one out and see if it starts then try the other.

take out any adaptor cards and see if it boots and replace one at a time.

Also try to ensure that your CPU is getting proper cooling.

Also try to ensure that your CPU is getting proper cooling.

Thanks mate it looks like F-secure Internet security suite and Norton Anti virus were clashing with each other. I uninstalled one of them in safe mode and now the problem seems to be gone. F Secure products do clash a lot with rivals as said on their support site. Thanks a lot for the help offered.

I'm glad you were able to get that figured out. :-) Really good job.

And it's not just F-Secure. Any AV software will clash with another AV software installed on your system. Rule of thumb: Only have one AV software installed and keep updating it.