I have a Sony music centre (Mini - radio, twin cassette / CD. Quite good
but maybe 15 years old). The CD seemed to have stopped working - it
displayed "No Disc" and made a clicking noise.

Last night I put a cleaning CD in it and - behold it started to play it.
However, on some CDs it still doesn't recognise them and play them - just
the clicking (lens hitting the CD as it tries to focus??). All the CDs are
original ones (not PC made). I recall from some years ago when I took it
apart to fix a Cassette problem that it is a pain to get to the CD - they
are so cheap now that I am wondering if I am likely to be able to improve
it - or has it got a terminal illness (weak laser or something?)