The suggestions by everyone is about as good as you'll get. You'll want to check the pins and give the contacts on the game a good cleaning with rubbing alcohol. If that doesn't fix the situation then one of the chips on the game PCB has probably died. The only way to check a chip (that I'm aware of) is removing it from the PCB and putting it into a tester. Other than that, you would want to inspect the traces on the PCB of the game. run a multimeter from contacts to points on the chip and such. It's a bit of work if you really want find the problem that bad.