Attempt #2 strange problem

[CAMILOGOD]

Ive already posted on here about a problem ive been having but I might have tackled it the wrong way so im going to try to explain this differently.

About a month ago, I custom built a pc for gaming. The specs are
HAF coolermaster tower
P8Z77-v LX motherboard
nvidia geforce gtx 560
intel core i5 3570k processor
8gigs of corsair vengeance ram
1tb HDD
thermaltake TR2 RX 750w 80+ bronze certified psu

At first, I would play games like crysis, skyrim, and other current games on high to ultra high settings with no problems, the games would run for hours at about 30+ fps.After a week or so, after about 30 minutes, the screen would go black, the computer would sit at idle and there was no way of getting out of it without shutting down (not through windows but pressing the actual power button) after about 2 weeks, I was having the same problem but now some games dont even last 5 minutes without shutting down. Ive tried a game like inversion with everything set to low and the resolution lower than my native resolution (1920x1080)

What I've noticed is that games up to 2007 will run fairly fine, sometimes the fps will be choppy, which it shouldnt be because a pc like this should be able to run games from that year at highest settings.

The steps ive taken are benchmarking the cpu and gpu

Cpu results: the cpu passed all benchmarks with flying colors

Gpu results: During 3dmark benchmarking using 1600x900 resolution(lower than my native resolution) the FPS was horrible at around 4.5fps, also the computer went black screen and idle like it did during gaming and I had to manuall reestart.

What im considering eventually is buying another psu since I've read a few reviews of the one I have and they are not very positive, and also replacing my gpu. The problem is I dont have the money right now and I'd really like to be gaming and I know a computer of this calibur should be doing a better job.

[hood6558]

Sounds like a GPU problem. I would pull the card and visually inspect it, make sure the fan spins freely and isn't clogged with dust, reseat the card and connect to power supply, then check the Nvidia site for the latest driver. Also, are you monitoring temps? If not you should be so you can tell when your expensive hardware is about to go up in flames. I use Real Temp and HWiNFO64, sometimes Speedfan (although Speedfan will sometimes show some crazy wrong temps, like CPU 147c). 4.5 fps is normal in those benchmarks for some of the tests. So I'd check for high GPU temps while gaming or benchmarking (over80c) and determine the cause.

[walterm]

No cooler is mentioned.
Are you overclocking on the stock cooler?

Check all power connections.
Is your motherboard on the latest BIOS? The video card?
I might carefully reseat the RAM and run memtest, just because it is easy.
Reseat the video card and change the power supply plugs being used (i did have a malfunctioning plug, on an admittedly much cheaper power supply).

Can you place the GTX 560 in another computer to see what happens?
Can you borrow another power supply to try?