How to repair the battery operated Ridgid screw gun?

I've had the tool for 12 yrs now. It has helped me build quite a few projects on my property and elsewhere.

It's pretty much stopped working properly. It was working while I working on a project, when I went to use it on the next screw, pulled the trigger and nothing happened. YES it did have a fully charged battery. (The first thing I checked). I gave the screw gun a "tap" against a board and it worked for another screw then acted up again.

Any idea of how to fix this beloved tool.