Make sure that the volume is loud enough to hear
Try another disc, to see if the disc is damaged
Make sure that the disc is a digital audio disc. Your player cannot play CD-ROM, CD-i, VCD, or DVD
For home-burnt discs, make sure that they are CD-R or CD-RW, burnt with non-packet writing software, such as Easy CD Creator. Select the Disc at Once option in Data Disk mode. Your player cannot play data in Universal Data Format (UDF)
Make sure that your disc is not a two-sided, CD/DVD disc (called DualDisc or Flip Disc). Your player cannot play DualDiscs or Flip Discs