alpine dvd changer won't read

2005 Alpine DVD changer reads CD, MP3, CD-r, but will not recognize a DVD.  It just skips right over the disc like it is not there....Tried a few setup issues, but still nada....Any ideas?

what is the model number of your changer?

I have not seen this problem on a DVD unit yet, but when the optical pickup on a CD mechanism begins to fail, they quit reading burned CDs and then eventually quit reading store bought CDs.  It is more difficult for the lens to focus on a burned CD. It is even more difficult to focus on a DVD.   Your unit not able to focus on a DVD leads me to believe the pickup is at the early stage of failure.  What fails in the pickup is the tiny shock absorbers that supports the lens and keeps it midstream of the focus range.  When the shocks fail, the lens lowers too much and the focus motor does not have enough torque to lift the lens and allow it to focus.  In the early days of the CD players when the pickups started to fail, Pioneer sent out a bulletin to all of their warranty stations.  The bulletin instructed you to turn the radio upside down, if the cd would play with the radio upside down, and would not play with the radio in it's normal operating position, the laser pickup was bad.   You may want to try your changer upside down and see if it works.