Power Supply Damages Desktop PC

Usernameis

Honorable
Nov 22, 2013
36
0
10,530
Hi.

1. I took BIOS battery and jumpers out, put them back. Plugged in power cable in, power supply and motherboard fans spins for 1-2s and stops. No more reaction. Dead.
2. Took another power supply from desktop PC, works fine, motherboard spins.

I had long time ago the same issues and symptoms with other PCs, when once simply replaced DVD player, and secondly replaced HDDs, and happened the same. The only solution I came up to replace Power Supply.
But why such things are happening?
Also, if I short two pins of Power Supply connector (green and black can't remember), and plug power cord in, it works, spins non-stop.