Can't hear anything through headphones

[emcquaid]

What gear are you using?

Mac. Audio Interface? Cables, microphones, etc.
Software? DAW?

How is your gear is connected?

Best way to test is to go into a solos session, then record and playback to see what you hear.

Dont' forget fundamentals like connections. Ports go bad, cables become unplugged. My headphones come unplugged sometimes.

You have verified your phones work with another source like music on your phone?