download this usb driver: http://dlcdnet.asus.com/pub/ASUS/EeePAD/nexus7/usb_driver_r06_windows.zip
go to the device manager , right click the nexus device and choose properties, choose "hardware" and then choose update your driver , choose manualy and pick the folder you opend the zip file to and press apply.
open your setting in nexus . go to : "about the device" , at to the bottom of the page and press it strong text7 times .
open the developers menu and enable debug with usb.
finally press storage from the setting menu and click the menu that apears at the top left corner. press the connect usb to the computer, choose the second option (PTP).
that should do the trick.
