I've been recording various multi-track sessions in Pro Tools, but I've just now gone back to one of my sessions and attempted to record a new track. I create a new track as usual, make it record enabled, and then play my instrument. However, the track does not record. The edit window shows no wave forms. The edit window shows a highlighted red progression as if it's recording, but no sound is captured.

And, by the way, it's not an issue with the instrument inputs, because I just successfully created a new session and an audio track with the exact same input. I did that just moments before going back to this older session and trying to add a track to it. So nothing has changed in my setup whatsoever.

I've closed the session and re-opened it, but it's the same problem every time. Maybe there is something basic that I'm missing. Maybe there is a different way that I'm supposed to record a new track after creating a session and saving it previously. But I know I've been able to go back and add new tracks in the past without this problem, so this makes no sense.

Nothing is muted, and I've set up the track EXACTLY the same way as the others.

I have only three tracks in this particular session and I'm simply trying to record a new version of a previous audio track that I laid down. I'm not trying to overwrite it, though. I'm just trying to mute it and then create a new track to see if it sounds better than the existing one.

Someone please help.