MTD 604 Starter Motor Won't Stop

My father up on holiday kindly went out to mow my lawns. Unfortunately he has lost control and driven my MTD 604 (model number 13AV604G671) into a fence post with reasonable force.

The weirdest problem to arise is that the starter motor turns over continuously regardless of key position and without brake on or weight on seat. The only way to stop it is to disconnect the battery. I have pulled the ignition/key assembly out of the dash and it turns okay and appears to be undamaged.

Any ideas about what is going on?

I think I would check the starter solenoid for damage, since key switch has no effect.

/\ /\ /\ /\ What he said.