Hi, charliearon,
Thanks for that - what you say makes perfect sense even though it is being fed directly from the mouse socket at the rear/top of the PC. I have sent for a hub which will be self-powered, hoping that this might correct the problem. If you would like, I could let you know what the outcome was when it arrives. However, this may be a few days because I have sent away for a faster HDD to help FSX along its way, and have dis-assembled my PC ready for its arrival. If it isn't that, then I might possibly investigate supplying power directly from the PSU (at the right voltage of course)
As regards the updates, service packs, etc, yes, I will get in touch with PMDG although this usually requires quite an effort because for some reason, PMDG appear to refer everything to their forums, and I have to say that I am not a particularly patient person when it comes to reading through masses of questions and answers. It's something to do with my age, I think!
Anyway, regards and my thanks to you for taking the time and trouble to write back, it IS appreciated.
Philhen.