Sounds like you forgot to give the antenna its periodic dose of Viagra!:p! Only kidding to make a problem a little easier to handle!
!
The Captain gave you good advice to check out the problem. I'll add that when you turn on the radio a circuit is activated that sends elec. to the antenna - if other checks do not solve the problem look at the radio's connection for the power antenna and the antenna circuitry inside the radio.
Good Luck!
Tom