If you can’t sign in, can you sign in on Safari? Can you sign in on a New Private Window in Safari (File-New Private Window)? If so, it’s cookies, and clear them in Safari via Preferences->Privacy->Remove All Website data, or if you know what you’re doing, remove the SketchUp cookies for 3dwarehouse. Then restart SketchUp and try again.
I just tried copy-past on a component, and it beachballed for a second, but worked fine. Any other details?