Finder can't authenticate even though I am the admin
Based on the list of accounts, it appears to be that you're not an admin and there is no admin account on your computer. You'll need to create an admin account by running Setup Assistant again.


  
  Boot into Single User Mode ⌘ + S.
  Mount the drive by typing /sbin/mount -uw / then ↩ enter.
  Remove the Apple Setup Done file by typing rm /var/db/.AppleSetupDone then ↩ enter.
  Reboot by typing reboot then ↩ enter.
  Complete the setup process, creating a new admin account.