Hold in the reset button on your Express until the status light flashes, then let up. It should reset itself and go through it's diagnostics. Give it a few minutes to reset itself. Open Airport Utilitiy and choose "Open other Airport Base Stations" in the upper left. You'll see your Airport Express there, and will be able to adjust the properties there. Make sure that you go to the "Wireless" tab and select "Extend a wireless network" in the "Network Mode" options. Then it will show up as a part of your overall network too, in your network map.