When in either the Mix or Edit window, at the top menu, select "Windows -> Show Workspace" When the new window opens, you'll see a chart with available drives. There are two columns labeled "A" and "V". On the row where your audio drive is (whether internal or external), make sure that the "A" column has an "R" in it. You can click on that box and it'll show you "Transfer, Playback, or Record". Make sure that "Record" or "R" is enabled. That should fix the problem.