I just purchased a used 2004 Sierra 1500 SLT Crew cab. It has a factory rear DVD. It didn't come with an owners manual and I can't figure out how to navigate the rear entertainment system. It doesn't have a remote (present). The DVD menu comes up but I can't move the curser. I can play what ever is the default, but I am not getting any sound out of the speakers or wireless headset. Anyone have this system and know how to use it?