Computer crashes when playing higher end games - portal 2, darkness 2

Just built this computer last week (first build). I was able to play Witcher, Half Life 2, Oblivion, Starcraft 2 on the highest settings without issue. Everything seemed to be fine until I ran certain games. When I launched The Darkness 2 demo, it froze during the launch video and then the computer shut down. I tried it again and it went to blue screen and said something like "Windows encountered an error with a clock interval, your computer is being shut down to prevent damage to your system" or something like that.


I tried playing portal 2 and encountered the same problem. Then I just went through all of my games to see what would work and what wouldn't. Overlord also crashed...but it just went to the desktop and said something like "This program has encountered an error and must shut down."


I tried running the OC scanner and stress test the gpu to see if I could reproduce the problem, but it only seems to happen when I try to launch certain games.


I'm pretty sure my drivers are all up to date...which makes me think it is a hardware problem with either the mobo or the gpu. I don't know how to isolate the problem and figure out if I've just done something wrong with the build or if I have faulty hardware.


Suggestions?


OS - Windows 7 home
CPU - AMD FX-8120 Zambezi 3.1GHz Socket AM3+ 125W Eight-Core
MB - ASUS M5A88-V EVO
RAM - Kingston HyperX Blu 8GB (2gb x 4)
PSU - Thermaltake TR2 RX 750W Bronze
GPU - EVGA 01G-P3-1460-KR GeForce GTX 560
HD 1- Corsair Force Series 3 CSSD-F60GB3A-BK 2.5" 60GB SATA 3
HD 2 - Seagate Barracuda Green 1.5TB 5900 RPM 64MB Cache SATA 6.0Gb/s 3.5"