Not sure if power supply or...

Basically about 2 weeks ago I bought a custom pc with parts chosen from me and help from some people, and got the employees at the store to build it for me.
At first everything ran smooth, games like skyrim and crysis were playing at just about fully capacity with no problems...after a couple of days, after about 10-20 minutes of playing, the screen would go black, the gpu fan would stop spinning and id have to reset the computer.
I turned down the specs on the games to see if it would help, and it did, but the same thing would still happen after a while.
I checked the gpu temperatures and they were where they are supposed to be when idle and when gaming, since at first I thought I bought a defective video card, but now im thinking it might be the psu since I read a review on it and it was pretty bad. Heres that the review said.
"Thermaltake TR2 RX 750 W is, according to our methodology, a flawed product that must be avoided at all costs. It can’t deliver its labeled wattage at high temperatures, but this is not the worst of it: ripple and noise level are way above the maximum allowed when you pull 80% or more from the unit’s labeled capacity (i.e., 600 W and above), overloading your components (especially electrolytic capacitors from the motherboard and video cards), which can cause your PC to present an erratic behavior (crashes and random resets) and, under extreme conditions, damage components."
which is why im here now asking if anyone has the slightest clue of what is going on.
Thanks for your time.
PC SPECS:
asus p8z77-vlx motherboard
intel core i5 3570k 3.40ghz processor
8 gigs corsair vengeance ddr3 ram
nvidia geforce gtx 560 graphics card
thermaltake TR2 RX 750watt bronze certified 80 plus power supply unit
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