Everyone tries to help and cover the bases first.
When you connect to a pc to transfer files you should get a usb connection notification on the panel, and a pull down option to change from MTP to PTP. Media/Photo transfer.
I haven't tried this usb connection yet (recently got a tethering plan) but I would think the pc needs to see the phone as a usb network device, so something has to be set in the phone first. It must depend on the sequence of settings then connection, but something to play with. I have a Lenovo W7 pc with good network troubleshooting software.