|Test with a borrowed monitor.|
Install HWMonitor. Read the temps (all) and the voltages (all) and post results.
The temperatures may tell what part of your system is having trouble and will make further questions more effective in diagnosing the problem. The voltages may tell us if your power supply is having problems. If one or more of the main voltages are higher or lower than +/- 5% from their nominal values or fluctuate as the power supply warms, it will tell us if your power supply is bad and in need of replacing. Values that are too far off can damage other components and if they are high enough can fry CPU, GPU, hard drive, and motherboard to name a few so it is important to catch it early if that is the case.
You have to be a little bit crazy to keep you from going insane.