Computer Shutting Off

[thwhisler]

Windows 7 Home Premium 64 bit, Desktop, USB Mouse, USB keyboard, 6 gig RAM (3x2), WD 640 Black, GTX 470,i5 750, TX650 power supply, ASUS P7P55D-E LX, CD drive, Wifi adapter

Alright,  I'm getting a very weird computer error.
When I turn my computer on, it get to the part where the splash screen for starting windows appears and then turns off. There is no error message or anything. Everything just turns off.
If I leave it alone for a couple hours, and then turn it back on I can get into windows, and It'll be around 10 minutes before it turns off. I monitered the heat one of those times, and the GTX 470s heat was 44c, i5 750 was 32c, motherboard was 33c and the hard drive was 27c. So, I figure not a heat related issue.
Ran a ram test. No errors. CHKDSK found no errors.
It has been working for a month before this.
 What could it be?


<Admin edit> Don't need to post newegg links to each of your products.

[Computer Hope Admin]

Whenever a computer turns off, it's often a heat related issue. However, you indicated you checked the heat and it appears ok. Make sure each of the other possible reasons mentioned in the below document are also checked.

http://www.computerhope.com/issues/ch000689.htm

Also since this was built make sure you have applied your thermal compound properly between the heatsink and the CPU.