You'll have to describe exactly what the problem is/let us know what you see.
If you see nothing on the screen at all, that could be a big problem. Or it may be as simple as a dirty disk. It is pretty common
afaik for the 04/05 system to fail. You'll find lots of posts if you do a google search.
I had a problem where the system wouldn't read the disk anymore. I sent it to Alpine, and $158 later it was fixed. Actually, that price seems to be what many others have reported as well. You just have to send the DVD reader (in the trunk).
Just so you know, the processing/DVD reading happens in the trunk unit. The screen up front is only for display. Like I said, if you don't see anything on the screen, that could be a problem.
$4200?

I think that's for the entire system. F'ing dealership. Thank God for sites like this.