The majority of the defective MD decks sold have the same problem. The disc is stuck inside or doesn't load correctly.
To fix this you need 10 minutes, some tools and a new belt
First of all, you need to unscrew the cover and access to the inner part. You'll then discover that the deck itself is maintained with 4 screws.
Unscrew them, unplug the 2 ribbon cables at its back, you have in your hands the heart of the machine.
Now locate the belt, not all the MD decks are the same, but there's only little differences. In this case, the belt is in the down left corner of the opening.
With a hook, or something else that will fit, take the old belt out and replace it with the new one.
Now it's time to replace the ribon cables, be careful and do it slowly, and make a test. The disc should now slide in and out without any problems.
Replace the deck inside the unit, put back the screws, close the lid,...
It's done, you have a fully functional MD deck.
I always take profit of an open machine to double check each and very single connection inside. Sometimes, problems are so easy to solve that you even don't think about it.
I like to treat all the connectors with DeoxIT D5 to avoid future issues. I do that inside the machine, and outside on the RCAs, coax, terminals, ...
Enjoy your deck !!