Hello all,
My problem has been solved so I thought I'd tell you my solution. I searched for a hidden drive that was using the drive letter 'J', I had been told that was probably where the letter was, and found a ghost drive (zero anything in it) with the drive letter "J". I used "Disk Management" to give the ghost file another letter, in this case "S". Tthat released  the letter "J" to be returned to its proper drive and sorted all my problems. I do confess that when I restarted the computer I had my fingers crossed though...
Best regards.
Ken

The more I learn, the more I realise, I know nothing!