iPhone not appearing in iTunes

I'm running the latest version of iTunes for Windows on my Windows 8 Dell Desktop (latest version, running in Classic mode). Suddenly, and for no apparent reason, my iPhone 5c has stopped showing up as a device in iTunes when I connect it. Instead, a File Explorer window appears, showing my iPhone, as if it were an external drive. I have followed all the troubleshooting steps listed in the document on the Apple Support site, to no avail. Can anyone help?

Thanks