...whenever I try to add a note, it adds one, but in a light blue bar instead of the normal darkish blue bar color that it uses. Then the light blue bar/sound that was added doesn't play when I listen to it back.
When you write notes on the piano roll, the note velocity defaults to the last note you clicked. It's likely that you are writing notes at very low velocity and so can't hear them.
Double click the bad note and change the note on velocity in the box that pops up. That should fix it. Or change the note velocity as shown below.
NoteVelocity.png [ 27 KiB | Viewed 500 times ]