Factory radio question in 2000 ML55
 

My factory radio gets stuck at one radio station and volume knob does not respond and none of the buttons work.
I tried removing the radio fuse and put it back, turned off the radio and would not turn on at all with the fuse back in.
So, disconnecting the battery and reconnecting it, seemed to work after I put in the factory code.
It again did the same thing now, the radio is dead again.
I again have to disconnect the battery and reconnect and hopefully the radio works again.
Any suggestions as to what is wrong?
Thks
Barry