Inside the computer there are pins with jumpers on it which look likethis.
maybe one of those has come loose and somehow fell off.
IF NOT
Then , your hard-drive has gone listen with the side of the case off to hear if there is any movement from the hdd.
If it's spinning then it's not that, there is a battery on the motherboard which is used in watches take that out for 30 seconds and then place it back in and start up the computer , If still no change then it's goosed i'm afraid