Thanks for the reply guys. Tinker-san, the problem isn't involved in any way to the system rebooting itself or hanging on the shut-down. I had already disabled the 'reboot' default that XP does due to some undesirable effects.

I'll try the advice about a back-trojan. That's pretty logical too since I do a lot of things on the net. BTW, if I disable cmd.exe, how will it affect my computer? Is it possible that it might completely obliterate my XP if I attempted it? As a computer novice, I don't really know what cmd does (though I think it stands for 'command').

Thanks a lot for the help!

PS: how do I take a screenshot of my screen?