This guide might help
http://www.asus.com/support/Knowledge-Detail/28/2/Nexus_7/D53452AE-143C-42F1-BDC1-7F168085F0D7/
Although didn’t with me as drivers were already installed.
I made sure USB debugging was on. And that MTP was on. Still nothing. So set MTP to Charging, wait for Windows to do the drive thing again. Then set back to MTP. Drivers do their thing again and there are the folders. Finally.
This might also be useful
