This issue is most likely caused by a defective belt, it loses its grip over time and doesn’t transmit all the motor power to the tray mechanism, you can watch this [link|https://www.youtube.com/watch?v=qxL82LHPtQE|video] or search in the internet on how to replace a dvd belt.
Also, it is possible to manually fully close the tray with the disk in it by pushing the right parts of the dvd mechanism, it’s a bit difficult without mechanical knowledge but it is a good way to check that everything is functional before doing anything.