Have you tried turning the motor over by hand? You know, socket on the crank pulley bolt?
You can also make the starter operate when it's not bolted down in free air. I might unbolt it and operate it in the air to make sure it still works. If you have it bolted up the way I guessed, you may have screwed up the solenoid. Shorting the battery across the solenoid would make it see much more current than it normally see. You might have melted the contacts in the solenoid. I'd do the free air test and make sure you can turn it over by hand.