probably a case where the components in your case moved slightly, displacing something. it happened once with my older (now disused) phenomII 955BE system.
you could start with doing visual inspection of the inside of the case, see if there's anything unplugged, plug it back in if there is. turn on the system and test. i'm not hopeful it'll be fixed that easy, honestly. if it doesn't boot, proceed with the steps below:
- unplug the power connector from your psu, press the power button on your case to discharge any remaining electricity.
- touch the side of your case to ground yourself, proceed to take out the components one after another (can leave the motherboard inside). don't cut corners and take only some out. think of it as reassembling your computer from scratch to make sure everything is seated properly, thermal paste applied properly, GPU seated properly (most of the time it's this, as cards these days can be rather heavy, and could displace easily if subjected to slightest of shock), all connectors at where it should be.
- reassemble like what said above. do a final visual inspection.
- cross your fingers, plug in the power cord, press that power on button.
if this don't work, there comes the troublesome part of identifying which potential components that maybe broken.
no siggy, saw stuff that made me sad.