I have only just installed Windows and haven't installed AV yet...=:o

I've cleared cache/cookies and re-tried

sync diagnostics confirms that no sync connection has been successful. This is not really surprising. From that Windows account it has never asked for which account to connect to....

No - it looks and behaves as though it won't connect but there's no visual error message. Anyone know if there is a way to see why the connection is failing?

Can anyone help with this please?
I've just done an reinstallation of Windows 10 Home with Opera v45 as default browser (of course!)
The PC has 2 user accounts on it (both Admin rights)
Each user has their own Opera account which worked fine before I had to reinstall Windows
Now, one account connects & syncs OK but the other wont even sign in (from Settings:Browser:Synchronization) When I click sign in, the Synchronization icon appears (all grey) and then disappears. The account is accessible via https://sync.opera.com/web/ though
Any suggestions?