Hello, this is my first time building a pc, and after plugging it in the pc would run normally (fans and lights on) for around 30 seconds before shutting completely off for a few seconds then turning back on and repeat. I've removed the ram and gpu and it still does it. Only when i unplug the 8 pin CPU power supply chord the pc would stay on. The monitor shows no signal when plugged in. What would be the problem?