One speaker dead

My audio system seems to have lost the drivers front speaker. It works fine for the nav. lady and when I get phone calls but will not put any sound at all through from the radio.

Any ideas's? Does it need to be reset somehow?

Thanks in advance,
Scott

 

More to the story..
The speaker started working so I started the nav. and once the voice starts, the raido goes away on that speaker but never comes back. At one point I could hear it try to kick in a couple of times after the nav lady stopped talking but it never quite made it.
My wife says it was sporadically coming and going as she drove home.