Not getting enough water into the ice maker. Could be a partially frozen supply line, restricting the total water input, or it could be that the timer needs to be adjust.
If the water supply tube to the icemaker is frozen. It will be a white rubber tube on the right side of the icemaker. Warm it with a hair dryer, remove it from its aluminum tubing, and make sure there is no ice all the way back to where the supply tube comes from the water valve. After thawing, your icemaker should start working again.
Now..... why did it freeze? Most likely, there is a restricted airflow to the back of the unit, which is need to keep that aluminum supply tube just warm enough to assure all the water flow OUT of it into the icemaker, and doesn't freeze up on contact. Make sure your coils and the airspace under the fridge are completely clean (vacuuum them well) and it should cure the problem.
To adjust the timer, follow the instructions here http://www.acmehowto.com/howto/appliance/icemaker/diagicemaker.php