I've been having issues with wow. Without warning, and at completely random times, wow will cause my computer to restart. Some times it's after 5 minutes of playing. Sometimes it's after 5 hours. I've gone so far as opening the side of my case and have a fan pointed in, but that didn't change the frequency of crashes at all. I have NO idea what's doing this, and even after reformatting and a fresh wow install I'm still having the issue. Any help would be wonderful.
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Check out the WoW Forums. This is a common problem with wow.
Friend had same problem awhile back and was able to resolve it from trying numerous fixes from there.
Does it BSOD? Does it appear to cut out and after a few seconds start booting again?
Try playing another game that'll strain your PC equally and see if it does it there as well.
Spec of your PC/PC model would be quite handy as well if you could.
Random reboots normally point to a hardware issue.
A bad power supply or bad RAM can cause a system to randomly reboot.
First, try running Memtest86+ for several passes and see what it reports on the RAM.