My Custom Gaming PC Freezes During Gaming Only?

I have searched endlessly through the internet and can't find a fix for my issue. I recently bought a custom built gaming computer from Ironside. The computer itself works fantastic, however I started playing Skyrim and it was freezing up. I figured it was a Steam issue because Steam is known for lots of gaming mistakes. However when the problem wouldn't fix, I decided to try it out on a new game. I tried The Sims 3, Minecraft, and other games and then I discovered this was the actual computer's fault.

These are my specs:

AMD Processor - AMD Athlon x4 760K 3.8GHz (Quad Core)
CPU Cooling - Standard Heatsink
AMD Motherboard - MSI FM2-A55M-E33 {2 DDR3 Slots}
Memory - 8GB (1x8GB) DDR3 1600MHz
Hard Drive - 1TB 7200 RPM
Storage Hard Drive - None
Optical Drive - DVD Writer
Graphics Card - Nvidia Geforce GTX 760 2GB
Power Supply - 600 Watt Power Supply
Operating System - Windows 8.1 64 Bit
Networking - Internal Wireless N 150Mbps

The game is fine on highest settings for about 5-20 minutes and then it restarts/freezes. Other people are having this issue but I haven't found a solution. If anyone could help or has anything similar happening to them please respond. Surely ironside didn't send me a dud…

Also, if you have an answer could you go a bit into depth because I'm not exactly a genuis (in case you couldn't tell)

Have you got all of the newest drivers?
Does an error message pop-up when the game crashes?
It sounds like your pc is crashing because it's not getting enough power so it just stops.