Happens quite a bit on Windows 7. The Leap Motion device is running nicely for a while, then you unplug it and plug it back in, and boom: no service. Simple solution is to restart the service.
Start > All programs > Accessories > (Right Click ‘Command Prompt’) > Run As administrator
c:\> net start LeapService
If something similar happens on Linux, where the Leap Motion controller used to work and just suddenly stops, check your leap daemon. ensure none of the daemons are running
$ ps aux |grep leapd . Kill all the daemons that are running
$ killall -9 leapd and then restart the daemon