Install the latest driver version for your device (if it has not been installed yet). You can download the latest drivers from the Drivers & Other Files page on the Native Instruments website.

Note: Make sure the device is NOT connected while installing the driver.
After finishing the driver installation, connect the device to the computer. Then start the Windows Device Manager:

Windows Vista/Windows 7: System Panel > Device Manager
Windows XP: System Panel > System > Hardware > Device Manager
Windows 8: Settings > Control Panel > System and Security > System > Device Manager

or go to the Tiles window and type 'Device Manager'
An entry with the name of your device should appear in both the areas Sound, video & game controllers AND Universal Serial Bus controllers.
Device_Manager_Entry

If your device appears as USB Audio or as Unknown Device or is marked with an "!" exclamation mark as shown in the screenshots below, you will have to install the driver manually:

In the Device manager, right-click on the device and select Update Driver Software... from the menu that appears.

In the window that opens, choose Browse my computer for driver software.
Note: In Windows XP, choose Install from a list or specific location (Advanced). In the next Window choose Don't search. I will choose the driver to install and click Browse.
Browse to the following directory: C: > Program Files > Native Instruments > *Device Name* Driver > Inf

(e.g. "Audio 4 DJ Driver > Inf")
Click the OK button in the dialog window to load the driver.

If an entry with the name of your device appears in both Sound, video & game controllers AND Universal Serial Bus controllers now, everything is set up properly