reply to bearcatnat
Re: Stubborn Laptop Wireless - "No Connections" I have also had the wireless antenna connector come partially loose on the wireless card causing similar problems. The connector only pushes onto the card so a hard knock or just vibration over time can sometimes shake it loose.
There should be an access panel you can open on the bottom of most laptops where you can verify physically that the small connector is on tight. A quick reading of the user manual or a Google search will tell you how to access the card in your particular laptop.
Someone mentioned, running inSSIDer to check for channel interference. It can also help identify this kind of problem as every signal will usually be way low or non-existent if the cable is loose.