Windows 7 - Troubleshooting reboots

I have a system that is experiencing three kinds of symptoms that I'm need to troubleshoot.

Reboots - The system reboots itself without producing any BSOD, it powers down then powers up directly.

Artifacts, flickering - An image composed of vertical lines appear on the monitor. The colour of the image changes from one time to another. Sometimes its just white or black. I have also noticed some flickering.

Unable to boot - Sometimes, mostly in combination with the two above mentioned problems, the system is unable to boot properly. It powers up but nothing more happens.

I haven't been able to find any consistency for these problems, the system can run fine for two days nonstop or it can reboot after 5 min, aside form that they all occur when the system is under moderate load (gaming). This in addition to the artifacts tells me that it most likely is a GPU hardware problem.

However, I would appreciate if someone could take a look on the dump to see if theres any information that might help.