Random shutdown and restart

[prk72]

I've officially thrown in the towel and am asking for help. I've built a HTPC, this machine will shutdown for no reason and boot itself back up. I don't know what else to do. On one test after installing Win7 and updating all the drivers from the MOBO CD it would shutdown just as you get to the sign in screen. I disabled "Turbo" in the BIOS and that would allow me to start up normally. Now it will shut down typically when watching a 1080p MKV movie running XBMC about 45 minutes into the movie. I don't have an issue with the heat of my CPU, typically it doesn't get over 55C, the max I've seen is 62C. The only adjustment I've made to the BIOS was to turn of the Turbo setting. This is what I have:

Gigabyte H55-USB3
Intel i5 650 @ 3.20GHz
A-Data DDR3 1333 2x2GB
WD 20EADS
LG DVD Drive
LG Bluray Drive
Corsair 550VX

Please help!

 

[prk72]

Well, I now know that my problem is only related to Windows 7. I installed XP Pro and had zero problems. I assume it must be a driver, not to try and figure out which driver.