Premiere Pro CS6, and later
Some users have trouble dragging a clip into the Timeline. One of three things can happen:
Make sure source video and audio is patched in the Timeline, then drag the clip to the Timeline. In certain cases it is not automatically patched.
In Premiere Pro CC 2015 (9.2) there is a bug preventing dragging any clip to the Timeline without the application freezing:
(Premiere Pro CS5.5, and earlier)
See this video: Why does audio not go to the track where I drop it?