If you've tried all the suggestions made by everyone and the radio still doesn't work, its safe to thro it in the trash!! RTR's usually come with crappy radios anyway, so don't expect it to last.

It may be easier to just upgrade the radio to something more reliable! Try a futaba 2PH AM if your on a tight budget or futaba 3PM FM (this is a an excellent radio for the $$).

Oh in addition to the radio upgrade, you need to use NiMH battery packs especially for the reciever and transmitter, a fail safe is also a good investment!