If you are having problems getting a CD to run its program, or read a file from it, or play music, there are many simple explanations.
Now that most people are familiar with CDs this first one is less likely, but make sure you put it in the drive label up. If you want to really challenge a PC support professional, put the CD in upside down and see how long it takes them to figure it out. If they suggest popping the cover, let them in on the joke.
Other simple reasons that a music CD will not work are that the sound is turned down or muted, or that the speakers have been unplugged. If you use a headset, did you leave it plugged in? Are the speakers plugged into the microphone jack by mistake?
Any CD that is scratched or chipped will either not work, or work sporadically. There are repair kits that can smooth out scratches and make unusable CDs work again. It is a good idea to make a copy of any data you want to keep, in case it is damaged bad enough to not be a permanent fix.
If the shiny material is exposed, the CD is ruined for anything but a coaster or other ornamental use. CDs that are cracked or split should not be placed in the CD Drive, or it could possible damage the drive.