PC shutting down while gaming

My PC sometimes shuts down while gaming. And when it is off it won't just come on. I have to wait approximatly half an hour before I can power it on. If I Try to turn it on after it just shut down nothing happens. If I turn the power on my power supply off and on. Then try to turn it on, I see the fans spin for a moment but it won't boot, nothing happens.
If I then wait for half an hour and turn the psu off and on it boots and it is like nothing happened. My specs are: i5 3570k, asus gtx 680 top, asus maximus Gene V, Corsair TX 750 watt psuasus xonar essence stx, samsung 830 256 gb, 1tb seagate barracuda. I have my steam games on my hdd.
It shuts down while gaming. After around one match of payday 2. One time it shut down while playing guild wars. And it happened while playing Battlefield 4. The first time it shut down it automatically rebooted, but that doesn't happen anymore. I really don't know what to do, the powersupply is good and has an high enough wattage. The system is about one year old.
I brought it to a computer store once but they couldn't find anything. (but he said he didn't do any testing with de videocard)  

Maybe your cpu is overheating? have you tried monitoring your temps or noticed it shutting off when playing heavy games?

maybe your motherboard is bad? since it doesnt reboot, and it sounds like a bad overclock?

cause what appears to be happening is that you need to wait for the cmos to lose energy and clear the settings so it can reboot again. i duno, try testing or replacing your motherboard battery.

That sounds more plausible than what i said

all good, it could be anything really :p even a bad HD

My gpu is getting around 65 degrees Celsuis while gaming and my cpu around 55-65, depends on the game. Today my pc just rebooted randamly while watching a youtube video. Just like I pressed the reset switch, but other times it is just like I turned my psu off.

That temp could be a bit high but i think its fine or at least not bad enough to cause problems. Start cheap and try replacing your cmos but if that doesn't help you might need a new psu.

The temps aren't high. 65C isn't a problem.

I brought my pc to a local computer store and they found out that it is stable with another power supply. So that probably was the problem. My psu is also making a buzzing sound but when I tilt my pc a bit it goes away. I was hoping this psu would be good because it is made by seasonic. But I will send it back for another one after only one. 

Could be a defective PSU