Alienware x51 HELP!!

I sort of recently got my x51 for Christmas, I have the Windows 8, $1,699 model. It's been a very good machine to me. Up until about 3 weeks ago, every time I will play a game, I get about 5-10 minute game time. Then the machine black screens and it shuts off, but the fans keep going ridiculously fast. I have to wait about 5 minutes until they turn off and the machine reboots by itself. I can still perform non- game related activities on it.  I was really frightened. This has happened every time I try and play a game since 3 weeks ago. The room the pc is in is far from hot. I don't think it would be an overheating issue, especially when it was working fine before.I have completely reset my x51 just in case it wasn't a bad file. I have made sure all the components are plugged in properly, I don't know what else to do. The only reason I wanted my x51 was to play games like battlefield and just cause but now all I'm able to do to check Facebook. PLEASE HELP!