Now nowhere in this have you said that you have installed the usb drives for your k750i, I understand that it works with your k810i, but each phone needs its own drivers. When i plug my phone into my gf's laptop, i needed to install the drivers for my w810i even though she had the drivers for her w550i already installed. So unless I am missunderstanding you, you may wanna make sure that you have installed the usb drivers specifically for your k750i.