Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
I do not know who Dr. Y might be, I regret to say. So I cannot direct you as to how to return to your previous session - perhaps it was not with JustAnswer.com at all.
I think that the gears or workings of the changer of your Sony device are jammed. Either that, or the quite common defect of the motor having worn out because the work it does is so high-friction and load-intensive.
Which the problem is, I cannot tell from your description. But it must be one of the two.
The next question I need to ask is, how old is your Sony device? measured from its date of purchase.
Then it is definitely out of Sony's warranty. And, be it noted, it's amazing it has lasted this long without trouble with the changer.
CD changers (whether by Sony or other maker, but particularly by Sony - not to imply any really defective manufacture...) are notoriously prone to failure. That yours lasted 15 years is an abnormal length of time, in my humbled opinion.
But the motor is likely to have failed, so I think it will have to be serviced for that, if not also for the mechanism having gotten stuck or being sticky and difficult for the motor to work.