On most extenders, the extender or signal light specifically shows whether it is connected back to the main router. If that light is off while the other lights are on, the extender has lost its pairing with the router. This usually happens after the router reboots, changes its channel, or if the extender has been moved out of range. Worth trying a WPS re-pair first, or a full reset and setup from scratch if WPS does not work. Beers is right that extenders can cause more grief than they solve, especially on 2.4GHz where they just rebroadcast on the same channel. If range is the actual problem, a powerline adapter kit or a proper access point on a wired backhaul gives much cleaner results. Dead on.