A good place to start would be find out whether the failure is in the ice maker (is the harvester moving through it's cycle?) or the water supply (bad water valve, frozen line).
That should get you started, I just went through the same situation and learned way more about ice makers than I had ever wanted to. In my case there was a mechanical failure in the timer module. | 
Icemaker does'nt work-water from door does 
