Computer keeps crashing

I have a problem with my desktop. Every so often, it will just shut itself off, without warning. This is becomeing a major irritation to me, as it will shut off when I'm in the middle of downloading things, or writing a paper, things like that. It's running Windows XP, and I'm sorry but I can't give any more information. If more is needed, please tell me how to find out what specific things are needed to help.

Hello,

This usually happens when you computer has malware or it's overheating. Does you computer have good ventilation?

The ventilation could be better I suppose, I'll move it to a place where it will get more, and see if that helps, thanks.