Sometimes the android devices and Windows 8.1 just don't get along and when you plug the tablet/phone on the USB port, Windows does not show it to you on the "Mi PC" drive list.
This seems to be because something broke on the driver:
On the Android device (5.0) check that the USB output is set up to "MTP":
So on the Window device manager you just uninstall the Android device.
So on the Window device manager you just uninstall the Android device.
Unplug and plug the device again and Windows will install it again.
No error is showed now on the Windows Device Manager.
And the "Nexus 7" start to show on the "My PC" drives:
Now I can transfer the files.