Problem with Display NAV Unit

[MyHummer2]

I just bought 2004 H2; it has the factory Navigation unit. I am having problem with the ?Navigation screen display. The radio and CD works fine, but there is NO DISPLAY, just ?a blank WHITE color (can’t see anything but a white light). I took it to the dealer and ?they said to change the whole unit. Another place said the display board is defected, and ?they have no part for it, any idea where I can find parts for a 2004 NAV unit or any ?solution for it...?
Any help, I would appreciate it
Thanks