Are you seeing no shortcuts at all, or only the SketchUp defaults (e.g. spacebar for selection tool, o for orbit, etc.)?
Reset All on the preferences->shortcuts panel should eliminate your customizations and restore the defaults. It does not step back to a previous customization, it resets all the way to defaults. If it did something else, there seems to be a problem with your Mac’s preferences management, which will take some deeper digging.