Q: Need help with my wireless network

I don't know how or why, but I went from having a nice wireless network in my house (with some drop off of signal in my bedroom at the far end) to NOTHING. I have an Airport Extreme that is 19 mo old, and just got an Express to extend the network. I tried once before to get that set up, but was not successful. Today I checked into it again, and found I needed to change some settings on the Extreme to allow for extending the network, and from then on (after restart) I lost the wireless network. I have been trying for 2 hours to get my wireless network back up, even replacing the Extreme with the Express, but still cannot get either device to show in Airport Utility. HELP!