Help! My App Store login just clocks and doesn't sign in!

Hi,

I just purchased a used Mac Book Pro, so want to install the latest updates, including El Capitan.

When I enter my Apple ID and password, the login screen just clocks and clocks and won't sign me in. I also cannot connect to iTunes from this MacBook. I DID get an error the first and second times I entered my password (fat fingers), but typed it correctly the third time.

My Apple ID is used on several other devices, so I really don't want to reset it. Is there a way to get it "unstuck" on this Mac Book?

It accesses the internet fine, so I know it's not a connectivity issue.

The only posts I found on this were from 2012, so looking for more current fixes!

Thanks in advance!

-Sue