I run Sierra unsupported on a late 2009 Mac Mini and have had no problems with it until now after trying to uninstall and re-install (unsuccessfully) Skype. The Finder is not working properly. I can't open the Finder window from the Dock nor will Finder - Go work on the menu bar. But Finder - File - New Finder Window does work and I can access Apps from there successully and also from the Dock. Repeated rebooting doesn't work except occasionally for a short time and I've even re-installed Sierra without changing anything. I assume the re-install happened but didn't encounter any setting up procedure though I didn't really expect it. So what's going on with either Finder or the Dock?