Won't crank.

I recently sold my 96 cavalier 2.2L to a buddy of mine. The thing is, he let it sit up for about 2 months (which told him thats not good for a car). Now it wont crank. It will try and turn over but wont. He said he was driving down the road and all the cluster lights came on. Like the check engine, water etc. That was about 3 days ago. When he was drivning home the car backfired and now it wont crank.

Plus before all this happen he said he was jumping it off and he hooked the jump cables up wrong on the car which made the starter smoke real bad. Could that be one of the problems?
Thanx.

Are you sure he didn't overheat it and seized it up?

jumping backwards is atleast going to blow a fuse/link have you checked?

Are you sure he didn't overheat it and seized it up?

Not sure if he ran it hot least he said it never did. But he did just put in a new radiator. He said he checked all the fuses for the cluster and all where fine. He said it was running fine till it backfired. I think it's the fuel pump myself. The fuel pump thats in it is from a 99 or 00 cavalier I can't remember. It came off a junk car. But it was a tight fit putting it in. Don't a car backfire cause it's not pushing fuel or enough fuel into the rail?