Having had the same problem as in Unknown in rs2_create_device Error, I'll repeat the solution here:
The problem appears to be that the Windows 10 April update has changed access permissions for devices such as the camera and microphone, restricting all by default to none.
Go to Privacy Settings. Select the tab "Camera" and turn on "Allow apps to access your camera".
None of the apps below need to be given permission, however now you should be able to find and access your Realsense camera again.