Hi,
Has BT worked before on your laptop?
'''If so''' what OS is installed? Have you checked in Device Manager that the BT drivers are installed correctly?
'''If not''', you may not have the BT card installed in your laptop. Here is a link to the service manual which shows where the WPAN (UWB/BT) card is located.
http://downloads.dell.com/manuals/all-products/esuprt_laptop/esuprt_latitude_laptop/latitude-e6400_service%20manual_en-us.pdf