These address a Disc player that ejects a disk it cannot "read".
1) The lens is dirty (don't blow in it, you look nutter and it does nothing to clean the lens,it just adds moisture to the unit).
2) Your transport slides are impeded some way or needs lubricant.
3) You have a scratched or incorrect format of disk.
These relate to damage:
1) You dropped or Jarred something critical in the transport, and the Lens isn't aimed correctly.
2) There is damage to the clamp, where a disk is not seated properly.
3) The drive motor has worn out, lost a winding, or cannot reach the appropriate spindle speed.
In any case you could open and spray canned air in the unit and see if you can make it work, although this is doubtful to work. More than likely you need to consider replacement or professional servicing.
Any optical based electronics need periodic cleaning and lube. You can minimize this by keeping dust from the unit with regular exterior cleaning. It is the dust that ruins the lube job on the transport slides.