If you are still looking for the answer, which I just discovered myself.... The BIOS, under the Wireless heading, is where you turn the Bluetooth radio on and off. At least on the Latitude D620 and D630. The big surprise is that you can (apparently) turn it on  in the BIOS, even if THERE IS NO BLUETOOTH CARD INSTALLED!   The bluetooth cardspace is at the far left under the bezel above the keyboard. pop up the right end and gently lift up the bezel to see if you have the card installed. It was an option, not standard equipment.
I've been trying unsuccessfully for weeks to find out how to turn on the Bluetooth adapter (turn Bluetooth radio on) on my Dell Latitude D620.  Firstly does the D620 have a built in Bluetooth adapter? I've done a search on the web and it appears it does. Also I see a Bluetooth symbol just above my keyboard, but it is not lighted up. How do I turn it on?  I went to Control Panel, Device Manager -> Network adapters, but I don't see any Bluetooth devices listed there. Do I need to install some software? I went to support.dell.com and downloaded the installer for Dell Wireless 350 Bluetooth Internal Module driver. But when I install it, it is tries to install the Vista Profile Pack, and it fails because it "Could not find compatible bluetooth chip on your system" and "DFU install failed with returncode 137".  Really hope someone can help me. Thank you.
How to turn on Bluetooth adapter in Dell Latitude D620?