Try your router setup per this forum's sticky. Defaults, then change the SSID to simple. One short word and then turn on WPA for security.
I've lost count how many times that helps.
I have a Dell Inspiron E1505 Media Edition, windows xp, laptop. This problem has been going on the last year or so. My problem is that I only have wifi some of the time. When I start up, the internet may or may not be available. It will show all the wifi networks in the surrounding area but it does not always show mine. And then again sometimes it will show mine but will say "unable to connect" Sometimes it is gone for a day, and other times it is on and off constantly, sometimes as often as every few seconds. Sometimes it stays on all day. It is very annoying. Dell says it is a software problem. I am not real knowledgeable with a computer but I am far from a beginner. Please help! Thank You,Mishal