|By any chance did you remove the ram module(s) and then re-install it/them?|
If you installed any ram module backwards in it's slot , your symptoms are exactly what results from that. The ram module that was backwards and the ram slot it's in are damaged instantly when you attempt to boot the computer, and both of them will never work again.
If that's what you did, you will see that there are some damaged or missing (they were vaporized) contacts on the ram module that was backwards, there are some damaged or missing contacts in the ram slot it was in, and there are probably also black carbon deposits in the ram slot and melted plastic there.
If you see that, if you clean off the carbon and remove any melted plastic that bridges contacts, the mboard MIGHT still boot when you have installed undamaged ram in an undamaged ram slot.