As you might already found out "Intel® Wireless Bluetooth® for Windows ver. 21.xx.xx" from Intel website will not work. Therefore should be removed as well as any other unsuccessful driver installations (!)

You can find drivers at Dell's support center, for instance "Intel 6235 Bluetooth Application" driver is available at Dell Latitude e6440 support page.

However even after installing you'll find few "Bluetooth Peripheral Device" with yellow exclamation marks and no drivers available at microsoft update. (I've got 4 at mine)

To fix this last problem you have to:

1. Open "Device Manager"
2. Right-click on the "Bluetooth Peripheral Device" => "Properties"
3. Select "Driver" tab => "Update Driver"
4. Click "Browse my computer for driver software"
5. Click "Let me pick from a list of device drivers on my computer"
6. From the list "Common hardware types", Select "Ports (COM & LPT)"
7. In the left column choose "Microsoft" in the "Manufacturer" list
8. In the right column "Standard Serial over Bluetooth link" in the "Model" list
9. A warning window saying that it is not recommended pops up -- Ignore it by clicking 'Yes'

(much thanks and all the credits to Andy Dandifer from answers.microsoft "Error: Bluetooth peripheral device driver not found" tread)

@shiz.ualand​ Thank you, I found the page for my E6420 XFR here: https://www.dell.com/support/home/en-ca/drivers/driversdetails?driverid=1jmyp

Network_Application_1JMYP_WN32_17.1.1411.504_A01.EXE

And