E6400 Latitude insists that WiFi switch is off

When I turned my computer on this morning, the Wireless Network Connection icon in the taskbar had a big red X through it, and when I tried to enable it, it popped up with a message saying "The Dell Wireless WLAN Card is still disabled. Slide the Wireless ON/OFF switch to enable it." This is despite the fact that the switch is actually on. I've tried a few simple remedies, none of which worked:

• Flicking the switch off and on
• Rebooting
• Disabling and reenabling the device through Device Manager
• System Restore
• Updating the drivers (it says that the drivers are already the best they can be)
• Running Windows Update

The Ethernet works fine (which is how I'm using the internet now :emotion-1:), but the WiFi doesn't work in either Windows XP (the native operating system on my laptop) or in the Ubuntu dual-boot I installed a while ago. Any idea what the problem is?

Thanks for your help!