So far I've tried replacing the:
GPU
PSU
HDD
OS
RAM
MB
CPU
Same problem every time.
If you have that many parts (enough to build another computer), then you should build that other computer and mine with it. When it works fine, then you should have bad main system and good parts system. Eventually swapping components one at a time between the systems (until the only thing not swapped is the motherboard in the case), the problem will move to the other machine, or you have a bad motherboard.