Why can't I log into the cloud from my mac?

See this article Get help with iCloud - Apple Support

Make sure in system preferences > date and time you should not change any settings .

Yes i have the same error - it knows the password is right (I even changed the password) as if i enter incorrect password it tells me so, but with correct password, it goes away, wheel spins but then nothing happens. Ultimately if i try often enough (dozen times or more) it comes back with 'unknown error' - ?

Did you changed any read and write permissions , in home folder , guest account , shared folder , are you having iCloud verification code with you , have you set up iCloud Keychain .

As if these are changed certainly the mac user will get trouble signing in icloud services ( like in apple id account , in tunes , App Store ) .

But to very clear without iCloud verification code it is difficult to set , and you must have Apple ID , iCloud id , your web mail address and their respective passwords , if Mac is connected to air port express - in this you must have wireless network password in your records .

Please post a complete screen shot of your iCloud account ie in system preferences - iCloud . is the box keychain checked and is options button also showing in front of it .

Note - hide your mail address and personal picture if it is saved .

Might be a corrupt .plist.

Do a backup, preferably 2 backups on 2 separate drives.

Quit System Preferences.

Go to Finder and select your user/home folder. With that Finder window as the front window, either select Finder/View/Show View options or go command - J. When the View options opens, check ’Show Library Folder’. That should make your user library folder visible in your user/home folder. Select Library. Then go to Preferences/com.apple.systempreferences.plist. Move the .plist to your desktop.

Restart the computer, open the application, and test. If it works okay, delete the plist from the desktop.

If the application is the same, return the .plist to where you got it from, overwriting the newer one.

Thanks to leonie for some information contained in this.

Hi - i have just been on the phone to Apple helpdesk for 2 hours, we moved various files etc and partly solved the issue, however the person i spoke with seemed to intimate its something to do with the OS high sierra security settings which require internet provider to allow it to connect? i may be over simplifying it but my issues did start with this and hence might be cause of issues. We had to reset keychain and this seemed to allow us further in but as yet no photos have been shared with my mac - though i can see them on my phone and iPads still...

They are calling me back tomorrow

Try going to System Preferences/iCloud and stop Photos syncing by unchecking the box. Wait a couple of minutes, then check syncing.

Last resort - have you tried signing out of iCloud and then sign back in?

See this article Get help with iCloud Keychain - Apple Support

Have you tried quitting and reopening System Preferences?

Restarting the computer?

I do not understand this - i go to date and time but do not change anything?