Jaysus! Enough on the flaming apostrophes!

Reasons not to be cheerful about CDs and their players:-

The lens for the laser can get dirty or scratched. A dirty lens can be cleaned. A scratched lens is dead.

The lens assembly (the bit that shines the laser) moves around somewhat like the arm of a record to follow the "grooves". But the "grooves" on a CD are much finer than a record, so it has to be very accurate. Eventually something will go wrong - maybe the player will get bashed, or the motors or track will wear out and the lens will no longer follow the CD properly. End of story for the player. Some CDs seem to be easier for player to follow than others, so you'll usually find on a nearly-dead player that it'll play all except one or two, then more and more will refuse to play, until you finally give up and chuck the thing away.

The CD(s) could be dirty. CDs have error-correction built in which can take care of the occasional scratch/bit of dirt/hair on the CD, but if there's just too much then it won't play, or it'll play but skip spectacularly in place. Some players have better lenses, more powerful lasers or better software which can deal with this and recover better from problems like this.

The CD is a CD-R or a CD-RW. CD-Rs don't reflect light as well as a standard off-the-shelf CD, and CD-RWs even less so. Older players had weaker lasers which were designed to work with normal CDs, but no-one had thought about other types of CD, so they just don't shine enough light on the disk to get a CD-R to work. All modern players should work with CD-Rs, although I suspect the lower reflection off the disk will make any problems with dirt on the CD worse.

That's the common problems I can think of anyway.

Graham.