Lost signal on Airport Extreme

A couple of weeks ago I downloaded the firmware update for my Airport Extreme. It's been a bit laggy since then but was working. A few days ago the signal started going in and out constantly. So I went back to the previous firmware. It started working again but by the next day it stopped working all together. I thought it might be my modem but I switched it for a new one and still no signal. The Airport is about 3 years old. I have a MacBook Pro with Leopard but I've tried a few different computers and phones and none of them pick up the signal. Any suggestions?