Headphones are not working for Monitoring Garageband 8

It's been some time since I recorded on Garageband 8.

My specs:

Mac OS 10.6.8

Garageband 8

I used to be able to plug my headphones into the tower headphone jack (in front) to monitor as I was recording in Garageband 8.

Steps I took:

Created new project in GB - imported song for guide track

Set my input source to the USB Audio CODEC (the microphone) - according to readout, it is recieving fine

Monitor - set to ON with Feedback Protection

In the TRACKS section (upper left) I have clicked the hedphone icon on both the song guide and the vocal recording track

According to readout, it's playing - but no sound comes through headphones

Went to System Preferences > Sound > Output

MUTE is NOT checked

Output volume is FULL

Set it to Headphones/Headphones Port (no sound came out)

Reset to Line Out/Audio Line-out port (no sound came out)

Reser to Digital Out/Optical digital-out port (no sound came out)

tried all other settings (no sound came out)

Tried headphones and jack for other programs (itunes, taply, audacity) and sound played on headphoens just fine

So, slearly, there's something not set right in Garageband. But Monitor is on, headphones are clicked, volume is up...

Help?????