[vishnu]

It was under load, connected hard drive

Just one hard drive might not be sufficient load to ensure regulation. If you're at all handy with electronics at the component level you could try loading it with a resistor/resistors, you can procure pretty much any resistor imaginable at digikey dot com.

[At20]

We're going a bit of question, is motherboard dead? And is it dead for good? Because this is main concern, psu can be swapped, but finding another motherboard is relatively hard and very expensive for me