WTFDproject. (the WTFD is for "Way To Fix Drones")
Have you connected the Q500 to the GUI to see what may be causing the issue?
Other Folks have encountered things like being in a "No Fly Zone" or trying to start the motors while the controller flight mode switch is in Return to Home position.
Will the motors start if you switched off the GPS support? Maybe the GPS fix is missing due to HW problems with GPS module. If the drone was out in rain, to disconnect and connect again all connectors of the motherboard is a good idea.