the way you make it sound,i think you turned off your wireless modem.there might be a switch on the outside of your laptop, its just a little toggle switch just push it and hold until it tells you onscreen that your wireless modem is on, i accidentally turned off my wireless modem and it took me like an hour to figure it out. another thing you can do is enable it from the computer. ok so open up your wireless properties for the network you are using. im not to familiar with xp but there should be button in wireless properties that says enable.

on vista right click your network and click network and sharing center. there should be a network map that pops up, now click view status, it will open up wireless properties then click enable,but if you can't see enable then click diagnose. windows will try to find the problem and if it does it will repair it for you.

hope i could be of some help

Make sure all the MS networking files are loaded and not corrupted

Did you try to reboot the computer