I changed my google password. I can no longer get into gmail on my mac anymore. I can get into gmail on my pc and on my mac going to gmail.com. They system preferences pops up with attached message (picture below). However when I click on "Next", the blue bar at the top just keeps scrolling. Nothing happens. Notice that this image is greyed out. Unclickable after I click on "Next". So there is no opportunity to even input my updated password. I have done it manually in the email preferences as well. 
Changed Google Password and can’t get into gmail on macmail anymore
gmailmail.app
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Best Answer
Try to re-enable the Gmail account from Apple menu > System Preferences > Internet Accounts. If this does not work, boot to safe mode and attempt to disable and re-enable from here. Allow about minute to see the account again.
Use safe mode to isolate issues with your Mac