I had success with this. Sometimes this is caused by moisture from humidity getting on either the disc detect sensor or the laser lens itself.
1) Eject any disc in the unit
2) Run the unit for 2-3 hours to dry out any moisture
3) Turn the unit off for 5 minutes
4) Turn the unit on and retry loading the DVD
If it plays, it shoud be "fixed."
I would try the above again if it does not work or the DVD is pixelated.
Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
HAM CALLSIGN - KC3FFW