Hi...
Starting with the basic questions... What type of CDs are you using ?
If they are RW that could be the problem as there are very few car-type players that will play CD-RWs.
Perhaps for later, a suggestion that may or may not appeal to you...
Try >
CDex 1.51 for converting your .mp3s to .wav and then burning the .wav files to a CD.
Yes, this would be better discussed in the Tips & Tricks forum, sooooo...