Why doesn't my pc find any wireless networks?

[Jamak]

I have a toshiba laptop that has windows xp on it. It was working fine until suddenly I couldn't go on the internet and in fact it couldn't find any wireless network, while my mac found about five and connected to my wireless network perfectly. does anyone know how to reset it or how to make the computer forget the password of my network so I can reinstall it. Please some one help