I looked at everybody's ideas, and none of the ideas seemed to fit my situation. My DVD player has been working fine for one month. I got a new DVD today in the mail. It froze, and then began to display the WRONG DISK message. Then, nothing would play on the player, All of the DVDs that had worked fine before, now would not play. They all said WRONG DISK. I tried reaching under and trying to clean the laser lens, but that did not fix the problem. I am not saying that this will fix your problem, but this is what fixed mine.
1. Place the DVD player on a table
2. Plug in the DVD player.
3.Push the OPEN button so that the DVD platter extends outside of the player (It now looks like it does when it is ready for you to put a DVD in it to play it.)
4. Unplug the DVD player. (Now the power is off, and the platter is still extended.
5. Remove the cover of the DVD player being careful not to damage the extended platter.
NOTE: With the platter extended, looking slightly from the rear, under where the DVD is spun, you will be able to see the Laser lens. It will be covered by the mechanism that spins the DVD. The lens will be connected to a mechanism that that has two rails on either side.
6. Grasp the plastic surrounding of the laser lens area and pull the entire mechanism toward the rear of the DVD player.
CAREFUL: DO NOT YANK THE MECHANISM BACKWARDS as this will break off the laser unit. This mechanism is being moved with the resistance of many gears. PULL SLOWLY AND FIRMLY, and the entire mechanism will move on the rails until the laser unit is clearly visible to you and completely from under the spinning mechanism.
7. Since the lens was clearly visible now, and easily accessable, I carefully and lightly cleaned the lens with a Qtip and alcohol.
8. Replace the cover on the DVD player
9. Place a DVD on the platter.
10. Plug in the DVD player
You will find that you no longer get the WRONG DISK message and your DVDs will now play properly. As I said, just reaching under and cleaning the laser lens did not seem to fix the problem. It was only when I moved the entire laser unit from under the spinning mechanism, and forced the DVD player to realign itself when it powered on, did the DVDs begin to play again.