The well may be silted up, or the pump could be held down there by minerals that have built up on and around the pump.
With the pump set on poly pipe and some rope, there's not much you can do.
Hitting down on the pipe is not going to do anything. The poly pipe will absorb all the shock, and will have no affect on the pump at all.
It may be a good idea to get a pro out there to take a look.
There may be something he sees that may have slipped by you.
With the pump set on poly pipe, your options are very limited.