What could be wrong?

Hi, I've been using airport express for a year, but lately the airport utility ceased recognising my airport express. No matter what I did, nothing changed.I took it to my friends house, to try it on his mac, and the utility found it and the strangest thing was that my macbook (at my friends house) also found the airport express in the airport utility menu. But when I took it back to my place same thing happened, the utility could not find the wireless device. What could be the causing this? I mean, it worked at my place before and now it doesn't, but it works at my friends house. Could there be something that interferes with the apple airport express frequency? Or something else?
Thanks in advance...