[SOLVED] My pc keeps turning off when I start a game

[BeefBoy]

Hi, I switched out my motherboard, cpu, ram, and got another harddrive (SSD). I installed the new parts and reinstalled windows on the new harddrive. When I tried to boot my pc It turned on and off 3 times until I came to a recovery bluescreen. I sent it to the company I bought the parts from and asked them to look into it, and they said it was Corrupt OS and reinstalled windows for me. They did some testruns to see if it was fine and it worked but when I got the pc it worked for like 10 min and then I plugged in my second screen and after like 3 min or so it turned off so I thought it might be the psu that couldnt handle 2 screens. I plugged the second screen out and turned it on and then it worked. I downloaded discord and all that shit, and started playing. About an hour in it restarted itself and now when I try to open a game it restarts itself. Sometimes when I try to turn my pc on it turns on and off 3 times and I get into a recovery bluescreen that tells me Windows wasnt loaded properly or something like that. And sometimes I can turn my pc on perfectly but I cant open a game. And since I dont have product key for windows 10 and only have a digital license. Im not able to reactivate windows 10.

My specs:
Motherboard - ASUS ROG Strix B360-F Gaming, S-1151
CPU - Intel Core i7-8700 Prosessor
RAM - HyperX Fury DDR4 2666MHz 16GB
SSD - Kingston A1000 240GB M.2 SSD
HDD - wd desktop blue 500gb SATA 3.0
GPU - Geforce gtx 750 (Vram - 984mb)
PSU - Cooler Master B500 V2 500W

I thought it was the gpu failing or something so I borrowed my friends gtx 960 and plugged it in and tried to start a game but it still didnt work. I think its either the PSU failing or the windows because my pc turns off right when Its about to go into windows.
But I was also wondering if I dont have enough cooling paste on my cpu if it can cause the problem?

 

[Achaios]

Could be either:

1. Faulty GPU
2. Faulty PSU

Remove GPU and stress test it in friend's PC with reputable stress testing software such as 3D Mark Firestrike.

If GPU works okay under stress in friend's PC, then it's your PSU.

 

[BeefBoy]

Could be either:

1. Faulty GPU
2. Faulty PSU

Remove GPU and stress test it in friend's PC with reputable stress testing software such as 3D Mark Firestrike.

If GPU works okay under stress in friend's PC, then it's your PSU.

I have already tried switching out the gpu in my pc with my friends old gtx 960

 

[Achaios]

In that case your PSU is to blame. Get a new PSU.