SAMSUNG HT-Z Plays DVDs but not CDs, Why?

[Old Sparky]

I have a DVD player that will only play shop bought discs so it is absolutely useless for CDRs.

The three CDs I've tried so far are all commercially recorded discs, although one was a Freebie with 'Vintage Rock' magazine. The manual states that the machine should play both 3.5 & 5" CDs, but makes no mention of CD-R or RW discs.