gratz on finally getting your playchoice. Probably need to check and see the optics are clean inside the gun. Clean the screen, etc. If none of that works, the optical sensor may be bad. It's been posted somewhere that you could take the optics out of a NES zapper and put it in the gun and it work with a lil slight modification to the insides of the gun. I got my playchoice-10 with gun awhile back and had to work with it a bit to get the gun registering every shot. Good luck.
Brad