Let me be the first to welcome you to the forum...
The nav unit you have... is it the E7008? Or is it the older two piece unit (display in the dash / nav unit in the back)?
Are there currently any discs in it now? Is the nav disc in it? Is anything blocking it from opening by chance? Does it make any noise at all when you hit the eject / load buttons?
Not having one sitting here in front of me, that's about all I can think of. Before taking it to the stealer, try putting it in diagnostic mode and see if any fail messages or codes come up.
Either way, if you get fail codes or not, I would pull the unit from the dash, and attempt again to see if there's something noticeable. If you don't get any different results, unplug the unit for a minute or so, then plug it back in. I don't remember if there's a reset button, but if so try that.
Good luck.
