re-connect everything
taking great care to avoid static build-up on your hands, remove and re-connect all connectore on the motherboard and on the device ends. Be careful which way round these connectores are, in other words do them one at a time. Then carefully remove and replace all memory units from their slots. Do not apply too much pressure on the motherboard. Finally, check for anyhting shorting, and such oddments as a loose screw behind the motherboard.
This is the most likely possibility after physically bouncing a PC around in a car. Good luck