I have the above captioned DVD player, recently bought used. It seems
to have a problem reading DVDs (at the moment I only have two).
Occasionally it will read the disc, but more often than not it gives
the "No Disc" error message. Audio CDs seem to be fine.

My first question is: is it more likely that the DVDs have degraded
or that the DVD player has?

My second question is: having looked inside the box, what I see
appears to be a standard computer DVD drive connected to the power
supply side with a standard computer power supply cable and to the
other side with a standard 40-pin IDE cable. The only notable
difference is that there is no Audio cable evident. If the DVD player
rather than my DVDs turn out to be the problem, would it be worth
trying to use a computer DVD drive in place of what's there now?

Any suggestions welcomed.