Sounds like it may not be fully charged. Have you tried calling Sonos for a better diagnostic?

I’d at least temporarily remove it from the charge base, and plug it in directly. Make sure that the plug that you have plugged in to the wall is of sufficient power, and working properly, too. There have been cases of people trying to use underpowered chargers that just don’t send enough through the system. 

Try pressing harder if all suggestion fails, some buttons are getting stiffed specially if the product is too old.