speaker question

[Corbusa]

My car has an after market stereo and the front speakers are not playing at all. If the amps on the radio are bad does that stop them from playing or just lower the volume ? The rear play but it sure doesnt sound very good , I mean it sounds ok but not great ... Thanks
also I read somewhere that its easy to fix the factory speakers that a Diode or resister is what goes bad ( any ideas ?) Thanks