I have 2 Microsoft Lumia 640 LTE phones running Windows Phone 8.1 Update 2. One of them has no SIM card - I use it only to access my home network, the other is a fully functional phone with a SIM card. The problem I have is that my Windows PC running Windows 7X64 will not recognize the fully functional phone, while it readily does so with the other one. When connecting USB to the fully functional phone, there is a double "bump" audio which indicates non-recognition and it does not show up when I open Windows Explorer, while there is a single "bump" when I connect the other, and it does show up in Windows Explorer. On my wife's laptop, however, also running Windows 7X64, BOTH devices show up with no problem. On my PC, I use a powered USB hub, since I have more devices than USB ports on it, but I get the same result when I disconnect the hub and use a port on the back of the PC for the phone. My PC is usually in the sleep mode overnight, but when I shut it down and try connecting the fully functional phone, Windows begins to search for driver software, but after a few minutes produces an error saying it was unsuccessful.
Any suggestions would be appreciated