Well just the threat of you being on the case has worked David! I tried a new project again just for the heck of it and there it was playing happily along with the track. And then I went back to the project I'm on and its working. Now I thought it was working at first and then stopped but that was just after I had switched to 10.5 so I was hazy about that memory. As I mentioned An apple tech took control of my computer and we tried everything including setting up a new user account and downloading logic again but nothing worked and now it has magically started. Makes me worry it's a glitch but many thanks for taking the time to help me . Fingers crossed I don't come knocking again.
Btw everything looks the same, icon lit up and waveform showing but now I can hear the loop playing so whatever was wrong is not obvious unfortunately.
All the best.
Joe