Your motherboard is bad if electricity goes in and nothing is going out...
The POST won't happen on screen, but you will possibly hear fans spinning and see some leds come on. It really depends on what goes wrong. A motherboard is a very intricate piece of work (lookit all those copper traces and components, any one of those could go wrong, geez!).
If your motherboard goes bad, you will likely know as it generally will cause burning on at least one of the components from excess electricity building up which will be followed by an interesting electronic burning smell and possibly some thin wispy smoke.
If you suspect your motherboard has gone bad, salvage any devices and components you can and isolate the motherboard if you intend to troubleshoot/resolve the problem. Assuming you know squat about electronic components (because you probably wouldn't ask this question otherwise), it's time to go shopping for a new motherboard and any parts it took to heaven with it. :D