I have posted this on the Windows 7 forum, but I'm also posting it here. 
Here is the link to the post on the Win 7 forum, which also has screen shots.
http://www.sevenforums.com/hardware-devices/348305-korg-nanokontrol-connected-but-not-seen-applications.html#post2905273
 
Unit worked a couple of months ago when I got it and even configured Sonar X3 for it.  I put it away as I have another control surface.  I got it out yesterday as the control surface I have has been flakey lately (a Behringer BCF2000) - which is too bad as clients are impressed with the motorized faders.
 
I installed the unit and the Korg MIDI driver detects it.  Also, Device Manager shows it as working properly.  However its not detected by the Korg Kontrol Editor or Sonar X3.
 
I've uninstalled, restarted the PC, reinstalled and no help.  I've uninstalled using Revo Uninstaller Pro program which also allows deleting registry entries, then restart the PC and do a new install but no help.  I even did a System Restore back to before I tried to install it yesterday and still not help. 
 
The kicker is it works properly on Windows 8.1.  The system I'm using is a dual boot with both Win 7 and Win 8.1 (but separate SSD's). 
 
I'm not sure where to go next.
 
Jack
 
 
 

Have you already checked that the device is not "disabled" in the device manager?
I had that recently: device connected, recognized, drivers ok, but no operation possible.
 
Have you tried to "delete" the device in the device manager? I mean first disconnect it, then find it in the manager (with something like "view all devices" option set) and delete it there.
 
Do you have other MIDI devices/controllers working in the system properly? That is to check nothing is severe broken in the Windows drivers stack.
 
Do you have some software installed which can "consume" MIDI devices? I mean some kind of software "MIDI patch panel".

Everything you ask or suggest has been done, more than once.  I'm a computer tech and this has me baffled.
Read my post and the accompanying screen shots on the link I provided.
 
MIDI works with a USB connected MIDI keyboard and both my BCF2000 and the MIDI port on my Octa-Capture.  MIDI works OK on Band in a Box, too.
 
 

midi device limit reached? device manager --> view --> show hidden devices, delete all the "ghosts"
good luck! :-)

Nothing directly or even remotely reference the Korg, except the correct entry in the Sound section.   I had been through the show hidden devices (several times) before.
 
No MIDI device limit reached as I've done most of the testing with just the Korg, the only MIDI device, connected.
 
One issue, and it may not really be an issue.  In Win 8.1, where it works, the Device Manager lists under "Software Devices" - Microsoft Device Association Root Enumerator, nanoKONTROL_CTRL(out) and nanoKONTROL_SLIDER/KNOB(in).  I don't know if this is something specific to Win 8 or if this is what is missing in Win 7 (but how to get it).
 
Jack

i'll take a look when i get home, never had any trouble in win7, multiple daws, mine's a v1 btw

On the Korg USB MIDI Driver, it reports User Mode Driver 1.14.00.04 and Kernel Mode Driver 1.07.00.01
 

Have you checked
http://www.korgforums.com/forum/phpBB2/viewtopic.php?t=69644
and other threads about Win 7 and NanoKorg in this forum?
 
PS. I am also a computer tech, but I sometimes skip something obvious... 

Wow!  Thanks for the link.  I'm going to try some of the suggestions on that thread.  Most of what is there I've done (some more than once).  The one that sticks out that I'm going to try next is to uninstall, including registry entries, reboot and then install it in a compatibility mode for Vista SP2 and see what that does.  
 
When I uninstall with Revo Uninstaller Pro, it does a search in the Registry and the string that they mention is one that shows up to be deleted. 
 
 

Well, a complete uninstall, including searching the registry and deleting anything that has Korg in it, reboot and reinstalling with the Vista SP2 compatibility did not work.  Back to the drawing board.
 
The sad part is it works in the native Win 8.1 without any Korg software other than the plug and play driver that Windows installs.
As noted this is a dual boot system so Win 8.1 is using the same hardware, USB port, etc.