Download, install and run HDMonitor.
Look at voltages and temps, at idle. Run a program to load the cpu and monitor temps and voltages. The run a program to load the gpu and monitor temps and voltage.
Look closely at +12 V in both cases. The +12V should NOT be below 11.4 V
To load CPU, I use prime 95 - NOTE, monitor your temps closely and be prepared to stop Prime 95 if temps get to high, will reach close to it's max temp in about 15 Mins - In your your case that could be much shorter. Prime 95 is safe to run for long time, just I think you may have a temp/voltage problem.
Prime 95: http://majorgeeks.com/Prime95_d4363.html
To max out the GPU, run Furmark in a window.
Report back w/temps and voltages.