Computer crashes seemingly randomly


Jun 1, 2016
My PC crashes when playing heavy taxing video games. It does so fairly often. Sometimes when I start a fresh game, I can get to play say 3 hours maybe then the pc crashes. I reboot, and then I can maybe get 30 min of play time and it will crash again.
The crash itself, is a bit strange, my monitor goes black, like there is no connection, I get sound for 3-4 seconds, then the sound loops or bugs, and then total crash.
I thought for a long time it had something to do with heat, but it crashes when my CPU is 45 C and motherboard 51 C to 55 C.
I've had my graphic checked, and they didn't find anything wrong with it, when stress testing.

This problem has persisted since I bought it, from day 1, and that's 3-4 years ago.
My friend built the pc for me, and helped put the components together, since I am not very tech savvy.

Geforce GTX 770.
CPU: Intel Core i5-4670k 3.4 Ghz.
Samsung SSD 840 EVO 250GB.
Kingston DDR3 HyperX Beast 16GB.
Windows 7.

It runs games flawlessly until crash.

Anyone has a clue what might be the problem?
Manufacture mistake?