Did the computer get banged at all.
Crossed wires, you would have heard a bang and so I'm quite sure that you would have mentioned it in your OP.
If the computer got physically banged a memory stick ( or two ) the GPU or an internal connection may have come loose, all plug ins need to be removed and reseated and likewise all internal connections need to be checked for security.
While doing the above you should check for anything that could be causing a short, a bare wire, a stray screw or a loose I/O plate being three things to check.
Worse case scenario here would be that there was more moisture than was thought and a system short has occurred,