Please help if you can,  a couple months ago I bought a car with this unit in it.  I have no mam

I have no manual or instructions how to operate it.  The nav seemed to work ok, the radio works ok,  it accepts a cd and showed on the screen that it was playing but no sound,  same thing plugging in a thumb drive,  shows tracks and shows track is playing but no sound.  I also bought an HD radio for it, but it doesn't get any stations.  a couple days ago the screen went black after it boots up.  the radio still plays and the nav says lost signal when going thru a tunnel, but nothing on the screen.  it did come back on for a day, but is black again.  it does show the Pioneer splash screen when turning key on then goes black.  any ideas?

Update:   The has come back on a couple times,  but after phone call the radio does not come back on until you turn key off and back on.  in the dark I can see the screen is not dead, just nothing on it.   About ready to junk it and get something new if I can't get any help with it.