So I tried hot swapping but none of the boards I tried could flash the dead BIOS chip successfully.
Now I plugged the dead BIOS back to the original board and it doesn't even power up at all. Absolutely nothing happens when I pushed the power button. None of the fans (PSU, CPU) were spinning, not even for a split second. Removed all non-essential components and resitted mobo, but same thing. Tried another PSU, and powering up without the BIOS chip but no help.
Do I have a truly dead motherboard? But how could it be possible, I thought only the BIOS chip is dead.