Hi Lynn - thanks for your reply.
I have two other threads running on these problems.
The first one "Random faltering, clicks and beeps in audio playback" has run and run. If you can be bothered looking through it you will see all the things that have been tried including going back to 2010 version, but whatever the problem is now seems to be embedded somehow because that would not work properly either. PG support also did a remote access session but they have not been able to fix it. They did offer to try doing another one but that has never materialised.
I believe this problem started after I updated to 2011, however I did very little recording between then and when I updated to 2012 so it wasn't a major issue and one I foolishly thought would be fixed if I updated to 2012.
The most recent problem is in the thread "No playback in CoyoteWT". Still ongoing.
My Cubase version is LE4. It doesn't render MIDI to audio, only VST instruments. It doesn't recognise .seq files either.
It's fast looking as if I'm going to have to salvage what .seq files I can to .wav or whatever and reluctantly abandon PT.