Android device is not connected to USB for debugging (Android studio)

If you are on windows, many times it will not recognize the device fully and because of driver issues, the device won't show up.

• go to settings
• control panel
• hardware and sound
• device manager

And look for any devices showing an error. Many androids will show as an unknown USB device. Select that device and try to update the drivers for it.

I had this problem with a Nexus 7 - it appeared in Device Manager fine but wasn't recognised by Android Studio. The device had USB debugging turned on. Eventually I noticed an icon in the top left hand corner that said "Connected as a media device. Touch for other USB options." When I selected this I was able to change from Media Device (MTP) to Camera (PTP) and then it started working.