We have been having trouble with our Airport Express. It is working very slow (takes about 1 min. or longer to load a page). The internet works fine when we plug it directly into the computer. It was working fine a month ago but now it won’t. I have tried resetting it and unplugging everything. We have had problems with this Express before (we had to unplug it fairly often just to get our computers to connect to it).
So, I would absolutely recommend resetting the Airport Express back to factory defaults (pressing the reset button for about 15 seconds until the light blinks 4 times), and reconfiguring it with Airport Setup Assistant. If you have already done that, you might try switching cables out.
If THAT doesn’t work, and if it’s under warranty, please call Apple to get a new one. If it’s out of warranty, might as well buy a brand new, freaky-fast Airport Extreme!