So ever since I got the car the navigation system never worked. The slider slides back and comes out.

And the screen also stays black but turns on. The door or whatever has literally been taken off so l don't know what's wrong. I'm pretty sure the dvd player works but doesn't have the disc

Please help: (

 

Edit: After closer examination of your pics, I just realized you have an aftermarket touchscreen headunit installed. That's why the Nav screen is dead. You need the OEM Nav compatible headunit to work with the OEM Nav screen. The screen is essentially dead weight now, pointless to keep, and probably not possible to get working with an aftermarket headunit.

It could be the video source or the screen. If you're truly hell bent on getting the OEM nav working again, your best bet might be to find a repair expert and have the unit sent out for a fix. I've never owned a nav equipped Z33, they're pretty rare, most owners ditch the system and go with aftermarket since the tech is really dated, but also the price tag to fix the original will cost as much or more vs. purchasing a modern aftermarket system.

Sorry I couldn't be of more assistance. Good Luck!
-Icer