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:
Another option is if windows updates are turned totally off on your PC. In this case even if you download the USB driver & try update it manually as described above it will not work. The only way in this case is enabling windows updating drivers automatically. Once you enabled this, remove the non-working driver from device manager & connect you tablet to the PC via USB cable. The drivers will be automatically downloaded & installed by Windows. This way worked on my Windows 7 PC.