Need help on potential graphics card problem (Not sure if it is graphics card)

Sceptiken

Commendable
Jan 1, 2017
5
0
1,510
It all started when playing Path of Exile extensively for a week, my computer started to crash mid game several times. I would have to turn off the power supply and turn it back on in order to turn on computer back on. However, this one time where I crashed I could not turn the computer back on and had to go into recovery mode. I tried to reset the computer but got an error message. Instead I reinstalled windows 10 and I had the same problem. I had several streaks on the screen and so I assumed it was the graphics card at fault. I replaced my Asus R9 270 with a GT 620 and I have been using my computer fine ever since. However, only using the older card for 3 days, I have experienced several crashes. Some are just complete black outs of the system. The LEDs, display, and fans would power off. Also, there have been one or two crashes that involve only the display turning off and the system still going. These have all occurred while in a game. Another thing to note is random flashes of black when switching to a different screen. What should I do to diagnose which part is at fault?

Edit: I just tested my R9 270 and it does not work in the other system.
 

Sceptiken

Commendable
Jan 1, 2017
5
0
1,510


I have the EVGA 500w 80 plus power supply. I've had used my system fine for 2 years.