X51 R2, crashes when playing games

Hi

Whenever I try to play any game with 3D graphics, the computer completely shuts off and turns back on. Everything used to be fine until I played Halo 2 on my alienware with a high resolution. Since that the computer never shows the game and crashes before anything is seen on the screen. I have played other games in the past (Fallout 4, GTA V) and everything performed fine.

I downloaded Support Assist, and when I click "Scan Hardware," all tests are completed except the "Advanced Pattern Test," which the computer also completely shuts itself off midway through the test. No warning whatsoever.

I reinstalled all graphic drivers and also performed a wipe to see if any of that would solve the issue. No change.

I did the PSA test and it said there was nothing wrong with any of the components. The computer is at least 6 years old, but it worked fine before I played Halo 2 with a high resolution (This is Halo 2 for Windows Vista). I have played this game on another computer with a high resolution and it was somewhat playable (moderate frame drop, but the other computer did not crash).

Specs:
OS: Win10 Home
Graphics: NVIDIA GeForce GTX 745
Processor: Intel Core i7-4790 CPU 3.60GHz, 3601Mhz, 4 cores & 8 Logical Processors
BIOS: Alienware A07