What's wrong with the radio?
Check to make sure your receiver antenna is securely attached. You may have to take the receiver apart to give it a good inspection. Outside of that you have to narrow it down to Rx or Tx. Try another receiver. If it is the Rx, try one servo at a time plugged into the receiver. One of those buggers may be loading the whole Rx down.
When doing a range check what are the results?