Unit can play cd's, but cannot play dvd's.

Unit can play cd's, but cannot play dvd's. Installed this in November, it was able to play dvd's until last week. I had a dvd with mp3's that used to work now it won't. Tried a movie that works in my computer, still no luck. I get the error Cannot read this disc. I reset the unit, tried a lens cleaner, burnt a new dvd, also took the unit out of the vehicle, checked the parking wire, tried grounding the parking wire, still no luck. Anything else i can try?