Well...first thing to check is if the TX light is coming on the front panel of your radio when you press the transmit button to talk. If not...time for a new radio.
If it is coming on...chances are it is an antenna/wire corrosion issue. If you have acess to someone with an SWR meter, you can check the output of the radio and the quality of your antenna connection. Alternatively...you can buy a spare emergency VHF antenna (a good idea to have anyway) and hook it up to your radio and see if others can hear you. That will identify if the problem is radio or antenna system.
The shakespeare emergency vhf antenna is available here for $44.