Laptop Keeps Shutting Off

I recently bought an Acer Aspire 5315, it came with Windows Vista, I removed Vista and instantly installed Windows XP. Now, the computer just shuts off for no reason, no BSOD or anything like that, just shuts off. I sent it in to Acer for repair, the replaced the Hard Drive and sent it back to me, even though I really didn't think it was a Hard Drive issues. So I get the laptop back, remove Vista again, and add XP and now its still doing the same thing. Is there any way that the reason its shutting off is because I removed Vista and installed XP? Sometimes I can hear the fans not working as hard and it gets really hard, is it possible that there was something in Vista that can control the fans?

Thanks