First major malfunction

Today the camper broke. I parked it next to the building I live in, but not as far from the street as I wanted. So I tried to move it a bit. When I turned the key to "start" it again, there was no effect but dimming the lights on the board. When I turned it back to "on" the lights didn't light. The voltage on the ignition lock was +5 Volts, on the battery was more than +12 V. I wonder what is broken...