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Ha ha ha. There is nothing like a good 'but'. As it is a Windows machine I run a backup program called Acronis which not only backs up data but also the entire disk partitioning structures as well as my OS, That means I can always 'revert' if necessary. Partitions, OS or individual files. Don't like doing it as it takes forever but never the less it works, and very well.
I shall install over the top as you suggest and report back. Thank you for your help.
Cheers
Alan