Can not login into my iCloud (shows Error message that i am already logged in), What can i do?

Hi there,

I am unfortunately unable to log into my iCloud because I always get the message that I am already logged in. I am therefore unable to access the iCloud functions. Notes and Safari iCloud works, but not calendar and reminders. It all started after my storage was really low but i deleted a few things from my hard drive so now there is enough storage again. I restarted the Macbook already. Does anybody know how ill be able to access iCloud again.

regards, John