PC reboots in certain high demand games

[ArtyomTDO]

So, this is a weird one, I've been having a few random reboots on my rig for a while, and only during 2015 has it hung at the Asus Boot Screen. It always does it while gaming, which would be understandable as I tend to play things such as APB: Reloaded and Cities Skylines on max-ish graphics, but here's the kicker - Other high demand games don't do it. War Thunder has never done it to me on max graphics, and neither has Kerbal Space Program. I've run memtest, cleaned my PC of dust, re-organised wires, and even monitored the temperature closely on both SpeedFan and a case temperature sensor, neither have gone above 50, mostly hanging around 39-40. The only thing I could think it being is a cheap PSU, but I'm doubtful due to the inconsistency across high demand games.
My specs are:

AMD FX8120
Nvidia GTX 660 (The Gigabyte OC Windforce edition)
Asus M5A78L-M/USB3
4 x 4gb Ballistix RAM (Not exactly sure on model)
And the worst part of the build, the PSU
"750W" CiT PSU.

Please tell me if anything else is required, and thank you so much for looking into this as it's rather annoying to have to miss out on some games I really like.

 

[rolli59]

It is most likely failing PSU if there are no BSOD's involved.

 

[ArtyomTDO]

You'd think so rolli, but it begs the question why some games that are on par if not higher demand would not trigger this? I'm definitely going to replace the PSU when I can anyway, as not to risk it completely dying. I'll let you know when I get the PSU if that affects anything, thanks dude