If I connect the device without the debugging USB activated, the PC doesn't recognize it, such as the device doesn't exist. Neither the classic sound which the PC does when you connect something to the USBs ports. Nothing, without the debugging USB my PC doesn't recognize nothing, and the device only goes charging, the notify of the USB connected doesn't appear, it could be because the PC doesn't recognize the device.
But if I activate the USB debugging my PC recognizes something. The auto-installation from Windows Update for the drivers starts (it says "Nexus 5"), but it doesn't find any driver on Windows Update. So I've downloaded the original Google USB drivers. I've gone on Computer -> Device -> Right click on Nexus 5 -> Update of the drivers. So I selected the unzipped folder but Windows doesn't install the drivers. It says it's impossibile to find the driver for the device, but I've selected the correct folder!
I've also tried to download the drivers with SDK Manager, but even in this way Windows doesn't install the drivers.
I've also tried to download the "naked drivers" from XDA, but that was the same result.
So I don't know how to do. Why Windows doesn't recognize my device?
My Nexus 5 is still with the stock firmware.