Your wireless radio is off can be due to two things:
1) Wireless has been disabled by the Dell wireless app.
Use the Dell wireless app switch which runs in Windows OS. So you can use the Fn+2 to enable wireless again. (If you need to reinstall it its found on the Drivers and Utils CD)
2) You upgraded your Bios and its now stuffed up your radio.
You need to flash your Bios with a compatible version. I found flashing to Firmware A04 gets the radio enabled again. (I did tried A01 and A05 and both no dice)
I found a tool to flash your Dell Mini 9 Bios. You need a USB stick.
Run the program and it will prep a USB stick to make it bootable with the Bios flashing tools.