I have installed Android Studio. Then I have updated the Android SDK. Now when I start Android Studio, this message pops up:
ADB not responding. You c
From the command prompt run the command adb kill-server. This will shutdown ADB and android studio or Eclipse if you were to use that, would show Waiting for ADB as you said.
Once ADB has shutdown down run adb start-server or run adb devices which will automatically start the adb service and show that your android emulator or development devices has successfully connected.