The side rails that hold the SB-900/800/700/600/400 down are some times lose and with a bump could cause the flash to move. You may need to have these rails bent down a little or use a metal shim to make a tighter contact.
One of the 3 outer contacts is the communication pin that indicates to the camera that there is an active Speedlight mounted. So if your pop-up raises when a flash is seated, either the flash has shut down or the contact to this pin has been broken.
You might want to touch the Speedlight to see if it hot or open the battery compartment and see if the batteries are hot. If they are hot, you are probably having a thermal shut down. Adding a fifth battery or power pack increases the chances of overheating the SB-800.