I had this problem today when I got my first Leap Motion controller to play with. Stumbled across the solution looking through the files. For some reason, the V2 installer app appears to install the 32-bit drivers but not the 64-bit. However they are packaged with the SDK.
Navigate to: C:\Program Files (x86)\Leap Motion\Core Services\Drivers
Then run the dpinst64.exe driver installer found at this location. After installing, the leap motion should start tracking immediately. If it doesn't, right-click the Leap Motion icon in your system tray, and choose 'Resume Tracking'.