Can't start John Deere LX172?

My Brother flipped my John Deere LX172 riding mower. It started up after he rolled it over, but after shutting it off again, it won't start.The Battery light comes on, but nothing else happens (firing, turning over, etc...). I got it to start once by grounding the solenoid out, but now when I try that, it just whirs and doesn't plunge into the starter.I tested the battery strength, replaced the solenoid and had the starter checked out, but the same thing happens. The dealer told me it could be a safety switch, but I don't have a wiring diagram and don't really know where to start testing the connections & switches.