Also one more question...

when you guys say PSU, I'll tell you what I did.

I've changed the main PSU today (bought the new one), and connected one GPU (which was working until now) to motherboard and Boom, now it stopped working too.
My motherboard is supplied by different PSU separately...so would this PSU be faulty? this PSU only supplies electricity to motherboard. thats it.

So can this kind of PSU which only supplies mobo, be faulty, and this kill GPUs?

also, I've tested those dead GPUs to other farm, but no luck....