Dell Wireless Keyboard and Mouse (KM636) - how to differentiate between Logitech's Unifying and Dell's Universal pairing
Resumen: Pairing information to help resolve the mouse/keyboard not working.
Síntomas
This product was initially launched with the Logitech Unifying feature, however, this has now been replaced with the Dell Universal feature instead.
Causa
Confusion can occur because of identical appearances of the two versions, leading to improper pairing and non-functional devices.
Resolución
How to Verify Logitech Unifying v Dell Universal feature
The easiest way to check the version and subsequent compatibility is to look at the logo on the USB receiver and compare that to the logo on the bottom of the keyboard and/or mouse. The Dell Universal logo comes with ‘’BLUE RING’’ whereas the Logitech Unifying logo is an ‘’ORANGE STAR’’. 
Dell Universal devices (Keyboard, Mouse and Dongle) are NOT compatible with any of Logitech Unifying devices (Keyboard, Mouse and Dongle).
There are cases where these Unifying and Universal devices have been mixed up in use and this leads to devices not functioning. If this happens, please check all the devices again to make sure all devices are of the same Dell Universal or Logitech Unifying pairing.
Once the pairing matches you may have to resync your devices:
>For Dell Universal – Resync with Dell Universal Receiver Control Panel software may be needed. This software can be downloaded from www.dell.com/support.
>For Logitech Unifying – Resync with Logitech Unifying Application software may be needed. This software can be downloaded from www.dell.com/support.
Dell Wireless Keyboard and Mouse (KM636) uses RF2.4Ghz wireless technology. It is NOT Bluetooth. There is no pairing button on the device and it will need dongle + the software to resync.