BSOD randomly, code 50, a, 124, d1, 3b, 1a

Hi, recently I have experienced BSOD randomly with different code. They are 50, a, 124, d1, 3b, and 1a. The code 124 showed up most often. Sometimes the screen just froze up or went black, then I had to reset the PC. I ran the memtest86 and it passed without error more than 10 times. The problem should not be about the graphic card neither as I tested putting a graphic card and the...