Upgrade screen blocking everything

If you are having issues with CCleaner 7 then consider going back to v6.39: How to Roll Back from v7 to v6.39
Follow ALL of the instructions, particularly about turning off the Automatic Updating and deleting ‘CCupdate.exe’.
If you do not follow those instructions then your newly rolled back CCleaner v6.39 WILL update itself CCleaner7 again.