This happened to me once and it just turned out one of the PSU cables was knocked loose from the mobo.
I once had just 1 pin of an IDE cable not connecting back in the day. I thought it was the motherboard, but it was just the cable... which I discovered after a week of trying EVE-RY-THING.
Years ago when tp4 lived in ghetto housing, Tp4 found a mouse that chewed through his vga cable.
Did you kill it? SAY YOU KILLED IT
hahahaha.. At one point considered setting up a trap and poisoning him, but deep down just not that type of person..
Tp4 is of the non-violent sect..
It was not imperative to end its life over the cost of new cables..
Eventually the mouse was eating dates off the kitchen counter as Tp4 came down to make the midnightly ramen.
Tp4 threw a thin steel pot over the counter attempting to catch the mouse underneath, sadly the lip landed on the mouses' back killing it instantly..
It was a very small mouse, no bigger than a sake cup.
Why tell the story TP, this seems unnecessary..
Sigh.. Well Tp4 felt very badly afterwards, having unnecessarily ended the run of a complex lifeform..
It was buried in the garden..