Oh, okay, Stuck Centering is a different issue. If you have not turned on the machine for a while, it will try to load updates to the machine, and that can take a while. Just let it finish before you try to do anything from the app.
You also might need to clean the camera lens, or check to see if there is a glare from bright lights overhead. It can interfere with the camera being able to see the Glowforge logo on top of the printer head.
If you are still having trouble with getting the machine to Center, there is a list of further tests that you can run at the link below that will help Support to find what the issue is: