does it say anything on it or have a symbol ?
looking at the manual it is probably the wifi button
that is supposed to be blue when it is connected to the wifi
if it is not connected you can try
A. just turning it off and on again and it might re connect
B. do the original setup again
the instructions are on this page
once that light is blue you might have to install it on your computer again as it might have a new IP address
to do that go to devices and printers
remove the printer
click the add printer button
it should find it on the network
you can then just click next next etc
and it will show up again and work.
i can log in remotely to do this with you if you want to pay a little extra for premium service.