Thanks Guys, your inpout most appreciated. The problem was installing software and not being able to access supplementary files, so is not "media" (as in movie) related.
I have just come off the phone to Dell who have come up with a strange story. They say that that a new machine needs rebooting several times for the drive to be recognised, which on all my years of mucking about with computers, have never heard before. I will not be able to test this until I go back this evening, but will report back. Sounds a bit dubious to me, but we can try it.
thanks once more,
Conan
PS I did wonder about File sharing being locked. That was an early thought, but all reports ok and was tried with all options. Was beginning to wonder if this wasn't some Microsoft Media Centre jewel regarding Digital Rights Management for a while, but that was maybe a tad cynical...