Thank you for your replies - yes, I had already flushed the cache but that didn't help.
I've now sorted this by:
1. Using Windows uninstaller to uninstall Power Tools X - I even deleted folders containing data from older versions of jv16.
2. Downloaded the .exe file for Power Tools X
3. Closed all open programs & disabled my anti-virus
4. Performed a clean install of Power Tools X
5. Clicked on 'My Account' to get my licence
6. Ran 'Clean & Fix my Computer' - & it worked!! (It took ages because Power Tools X hadn't run properly since upgrading to Win 10 in mid-Feb)
7. After re-booting, my pc scores were back up to 100% again. Phew!
8. The scores went down significantly (but nowhere near the 1% & 2% that they had been) when I re-enabled my AV so I added jv16 to the list of exclusions, ran 'Clean & Fix my computer' again & now the scores are back up to 100%.
I can only assume that for some reason my old install of Power Tools X couldn't cope with the upgrade of Windows from Win7 to Win10, despite being the latest version itself, and was further hampered by my AV. All seems well now, though.
However, I have to say that, apart from the reply below, I have still heard nothing from Macecraft support. So much for paying extra for VIP support - I won't make that mistake again!