Just wondering - did you install the CPU / heatsink yourself? or did you buy the mobo with the CPU seated, installed, etc.?
I would also say to go through your entire system and make sure everything is in tight. RAM, graphics card(s), power cables all seated nicely, all pins in as they should be.
Hoped you could try another PCI-e slot, but looks like your mobo only has one :-\
Part of the problem is in order to diagnose this you may have to start swapping parts out for new ones - one part at a time. If there's a way you can get a hold of another card and try that, that'd be a good start.
In my experience, it ended up being my heatsink not seated properly and I had to even out the layers of silver compound. Then after all that troubleshooting it ended up being my video cards were overheating.
Is your video card fan functioning properly?
Are the games up to date also? Have you tried to dumb down the graphics settings? crank them down to bare minimum and see if they still freeze.
It's a very tedious, facepalm-ing business, lol... but you will learn ALOT about this stuff by your mistakes, trial and error, etc.