CD-RWs and CD-Rs as you probably have noticed, are considerably different in colour from regular shiny CDs. If your CD player is on the lower end of the spectrum, or slightly elderly, it may not be able to adjust it's laser output power to be able to get a reading off the CD-RW or CD-R. The different colour of the disc reflects a different wavelength of laser-light than a shiny-silver commerciallly released CD would.
If you have mastered the disc properly to play as an audio CD, then I would recomend trying to play your disc in any other player if you haven't already. Newer and/or more expensive machines adjust the laser output to sufficient power to get a reading off of disc.
If that doesn't work, try a different brand of media. Different companies use their own technology and formulation of the material that makes up the disc. Perhaps your equipment might have better luck with different materials.
If you are are trying to use CD-RWs only to save a few bucks, you may discover that your CD player can't use them. If you are really unlucky it may not even handle CD-Rs either. If your computer can read the discs you make, chances are the discs are just fine and your CD player is to blame.
First try playing your discs in a different machine. If it plays, then this will tell you your CD player is to blame. However, if you don't want to part with your CD player just yet, try a different brand of CD-RW or CD-R in the hopes that the different formulation of the disc will work in your machine.
I hope this helps!
