This is one of more weird solutions I have ever "found." I reinstalled the WiFi mini PCI-express card in our Toshiba 230D laptop and found the hardware radio was permanently off. That means I could not connect to any WifI network. I thought that I had a bad card, but the Intel Wifi Link 5300 drivers installed fine, and were properly running. So the laptop and OS "sees" the card but the diagnostics said "radio is off."
I found this thread that claimed to "tape over" pin #20 to force the hardware radio to be on all the time, regardless of what the laptop hardware was telling the card. This makeshift solution, worked like a charm. Not a driver issue, not a BIOS issue, not a Windows issue, but a strange issue with a broken hardware switch in the laptop. The manual "override" was the perfect solution.
Your mileage may vary.