If the problem is only with the Finder, you could also try to move the Finder plist file out of your Preferences folder. Just move it to your desktop. The Mac will create a new plist file when you re-start. Just go to your user Library > Preferences > com.apple.finder.plist. Move that item to the desktop. Then log out and log back in. See if the problem stops. If it does, then your old plist file was damaged. You can then safely discard that plist on the desktop. Important: by removing your plist file, any Finder settings you had made will be lost.