How to enable the ethernet port on airport express 2nd Gen?

Hello,

I bought the airport express so I could extend my timecapsle wifi network. The airport express seems to work great when using the wifi, but as soon I plug my computer into the ethernet cable the unit begins flashing the amber light. This is my second airport extpress. I returned the first one not realizing the wired connection was causing a problem. How do I configure the express to act as a wifi extender as well as allow me to use the ethernet port for my computers hard wired connection?

Thanks in advance,

Michael