if you're on the home screen, then pressing the 'hey, chumby' button (I'm sure there's some more proper name for it) does nothing.
if you *get* to that screen, then the chumby is activated already.
was it yours before we all had to climb into the lifeboat back in 2013 when the old service died?
if so, it's still registered on your account.
if you got it while we were in the lifeboat, then it's activated to someone else.
press the gear in the upper right, then device info and see who it's registered to.
if not to you, then you'll need info from that screen to enter into the 'deactivate a chumby' page on the webpage.
after deactivating it, reboot, then you can activate it as yours.
Cleaning up any loose bits and bytes.