whats wrong with my van?

i have a ford transit auto. i had the starter motor replaced around 1 year ago but have still had starting problems. i was advised to give it a tap ligt tap with a hammer which works, however yesterday it would not start regargless of tapping it. i tried tapping it while someone turned the key, it started to spark furiously and looked like it was about to catch fire. i hqad to get the aa out to recover it home. any ides on whats wrong with it.