The first thing I would do is check the batteries and contacts for corrosion. A quick, gentle clean with a fine wire brush might clean off any corrosion. For that matter, I would check for corrosion on other parts of the board as well. It could be that one of the chips has been shorted out and destroyed, in which case a repair would be very difficult. I guess if there's no corrosion or you clean it off and it still doesn't work, you may just have to bite the bullet and get a new one.
Good luck, hope you can get it fixed!
Regards,
Matt