Well, I'm going to assume you are running wireless-G. Many things could be interfering with the frequency. Since it is on the same frequency as microwaves and cordless phones. But you said it worked in the past. Another possibility is that someone else in the area recently got a wireless router and is using the same wireless channel as you and causing interference. Try logging into your router and changing the channel.

Also, make sure your network is secured because if so many other people are connecting to your wireless network it could limit your speeds and connectivity dramatically.