Computer Boots Itself 5 Seconds After Being Shutdown?

today I was cleaning around my computer area and well was dusting where my computer sits and I pushed it too far out and it fell and hit the ground. It was on too and the monitor lost signal even though the VGA cord was plugged in...Since I couldn't properly shut it off by going to start etc etc I just held the power button till it shutdown..I thought my video card got loose so I hit the kill switch unplugged it and checked everything,but it was all fine. When I plugged it back in,it turned on and well kinda lagged on start up,more than usual...I figured everything was fine until I shut it down and after it was off like 5 seconds later it turned on by itself?? I checked my motherboard and components for any damage or cracks but couldn't find anything. Now this I do not mind,i'm just afraid that it'll cause damage to my PC or cause my motherboard to fry or something because now in order to keep it off from starting byitself I have to shutdown then quickly hit the kill switch,sometimes I dont do it fast enough and the computer slightly turns on,too fast to stop me from switching it off. Also when I hit the killswitch to off and then switch it back on.the pc refuses to start itself until I push the ON button and shutdown again.