How can I kill Finder if it's not responding?
Answer found here.
Open a terminal, and move the saved settings from Finder into a backup folder just in case:
mv ~/L*/S*/*finder.savedState Desktop
Then, you can Force Quit Finder as usual using Command + Option + Esc, or use this handy terminal command:
killall Finder
Then, assuming everything looks good, you can delete the finder.savedState folder which has appeared on your desktop.
You can relaunch the Finder.
Just press ctrl + alt and right click on the Finder icon on the Dock. Then select Relaunch and it's done.