CCleaner-ing several times a day.

[Procrastinus]

This may help recovering your Windows key: https://support.microsoft.com/en-us/...1-a806abf0a886

[Mr Optimistic]

Run sfc perhaps ?

[Loose rivets]

If you upgraded to Windows 10 for free from Windows 7 or Windows 8.1, you should have a digital license instead of a product key.

I think I'll leave well alone until I've got a newer PC. I've Bookmarked the site, thanks.