why do cd players "sometimes" not read a disc?

Thanks Jafant. I have been pleased with its sound; but I found it benefited "dramatically" with ac isolation and conditioning.
I found conditioning and isolating the ac provided a quite remarkable transformation.
It makes me very curious about what internal parts related to power supply should be upgraded, and how.

I find moving the disc around in the tray can result
in it playing. What gives????? Can it be dirt on the laser?