Look at the four dip switches inside the rempte, and make sure they're still set to where you set them when you installed the fan. I dropped my remote and thought it was trashed, but two of the dip switches on the remote had just been thrown into the off position. I set the mproperly and it worked fine.
If you don't remember where the dip switches were supposed to be set, you'll have to remove the yellow remote control receiver from the fan itself and see where they're supposed to be set. Hope this helps!