Cannot Access iCloud Account

Up to 2 days ago I had no issues in accessing my iCloud account at the address https://www.icloud.com/Since then I receive the following alert when trying to login to iCloud "Connection Error. iCloud encountered an error while trying to connect to the server."

I opened my iCloud account in System Preferences, deselected all services e.g. Mail, Notes etc before logging out of my account. I then closed System Preferences and re-opened it. On opening iCloud I was prompted to log into my account. I entered both my Apple ID and password before hitting the Sign In button. The scroll wheel turns continuously, but I cannot enter my iCloud account. After about 15 seconds of scrolling the password field becomes blank i.e. the password disappears, whilst the Apple ID still displays. I am confident that I am using the correct Apple ID & password as I managed to accessed my Apple ID on line with these details.

I have also tried to set up an internet account using iCloud and the new entry displays with the word Inactive below it. I can then see the iCloud services, but suddenly the iCloud account disappears – please see attached screen shot.

Over the weekend I downloaded Malwarebytes protection and have also uninstalled this application earlier today. Still I cannot access my iCloud account.

I have tried rebooting my iMac a number of times, but still cannot set up my iCloud account. I have also tried resetting NVRAM (turn Mac off and on re-starting it, immediately press and hold the Option, Command, P & R keys until I hear the second start up sound).

Please assist.