Problem: Asus Nexus 7 not recognized by adb when correctly installed and connected
Setup: Asus Nexus 7 tablet Windows 7 64 bit OS
Steps taken:
After downloading the USB driver using the SDK manager, you can speed up the search for the new driver by telling Windows to look in the C:\Users\jdaehn\AppData\Local\Android\android-studio\sdk\extras\ folder (and sub-folders, in my case the drivers were in C:\Users\jdaehn\AppData\Local\Android\android-studio\sdk\extras\google\usb_driver)