Hey Mr. S.
Are you using windows 10?
If so, have you fully updated it?
Your previous configuration had windows 8, but are you sure of which software has been installed? How about Windows updates on this machine? Its possible that you are missing something in your newly installed windows that came from an update on your old machine (depending on how new the installation is, it may take a few days for it to get all of the updates it needs).
Thanks for the reply. Using Windows 8.1 Pro, which is definitely installed. All updated after each re-install too. I't driving me mad, I can't see any difference from before the re-install. Miner config files are the same as before, indexes correct and cpu mining disabled in the config.