I've had a similar problem for some months after over a year of normal operation but with a Nexus 4 Android (now Lollipop) phone and an Acer laptop running Windows 7. The Nexus would not show up in Windows Explorer in MTP mode, only PTP mode. That is ok for moving photos over to my laptop but not for making a backup of Android files, or data such as an exported Contacts list. On revisiting this problem and finding this page I did the following:
- Plug Nexus 4 into laptop (laptop acknowledges the connexion with its sound-effect)
- Go to Control Panel > Devices and Printers and click on Nexus
- Select Hardware, which shows Acer ADB Interface -- this seems to be what was wrong
- Go to Control Panel > Drivers, select Acer ADB Interface and delete it
- Unplug Nexus 4 and plug it in again, Windows goes off to find a driver for it
- Windows then installs a Nexus 4 driver, not the Acer ADB driver, and all is well.
Strangely, the Nexus driver has an earlier date and a lower version number than the Acer ADB driver had, suggesting it had somehow got upgraded. Perhaps I needed the Acer ADB driver for something, but I'll worry about that when I find out what.
