Random shutdowns

So i built a new pc a while and everything was smooth sailing till recently. This is only happening when i'm playing BF4 as far have noticed. Basically it auto restarts after sometime of playing, and its random too. I can play 3-5 games with out a problem somedays and other days the pc restarts its self mid game. Thought it was a thermal problem so i re-applied the thermal paste a week ago,but still no luck. During idle time the temps are around 35-45 and during load its 60-70. Hope you guys can help.

Here's the specs:

CPU:Intel Core i7-3820
FAN:Asetek 510LC Liquid Cooling System
HDD1: 2TB
HDD2: 1TB
MEMORY: 8GB (2GBx4) DDR3/1600MHz Quad Channel Memory (Kingston HyperX)
MOTHERBOARD: ) ASRock X79 Extreme 4 Intel X79 Chipset
VIDEO: NVIDIA GeForce GTX 780
POWERSUPPLY: 650 Watts - Thermaltake SMART Series

sounds like a bad power supply. check all your cable connections?

Any wires i should check particularly?

I just rechecked the cables and everything seems ok.

PSU is not good enough. You have only 50 watts over the minimum. So you are putting a LOT of stress on the PSU.

I'd have to agree with this, the only other think I could think of is if your reset leads to your motherboard are somehow loose or shorting out.

I also think that the power supply is being overloaded and shutting off.

Updated the PSU to 850w, no random shutdowns for the past 6-8hrs of gaming. Gonna test for another day or 2.Hope it's just the PSU and nothing else. 

850w is plenty.  You can overclock with plenty of wattage to spare.

Everything is back to normal, no more random shutdowns :)

Thanks everyone for your help.