Computer restarts itself after shutdown

[optimisticgadgeteer]

I believe this is related to software that will allow remote start of a computer.

I'm running Windows XP serv pk 2, and when I shut down my computer it will restart itself from between 5 sec and 2 minutes of shutdown, but only when connected to the broadband box.
My initial assumption was there was a virus/trojan horse/whatever, but three different antivirus programs have either turned up nothing or not solved the problem.
I have reason to believe someone who has access to my computer has loaded remote start software, how do I find out what program to look for to uninstall to solve the problem?

Thanks for any help and good days to all...

optimisticgadgeteer