The disks also may need to be "Finalized" after being burnt if they are CD-RW's. This essentially turns the CD-RW into a CD-R by burning an extra layer of data that allows more conventional audio-cd players to read the disk. Without being "Finalized" any burnt CD will not play in a regular audio-cd player, and afterwards all of them should (Assuming the burning process worked right, which isn't always the case.)