Why can't I hear audio while recording?

I currently am using Mac OS10.3.9. I tried recording with both the stable and beta versions of audacity. I record with a mic that plugs into a regular Mic Jack in the back on the G4 tower. My problem is that I cannot hear sound when I record with audacity. I mainly record rap music, so this poses a very big problem and I have been unable to record for months now. How may I fix this problem?

In Audacity’s Edit → Preferences → Audio I/O menu, make sure “play other tracks while recording new one” is checked.