2000 z71 front axle issue

[70stroker]

Alright guys me and a buddy took our trucks to a off road park today. he has a 2000 z71 chevy, while climbing a pretty steep hill on some rocks you hear a loud pop almost like a ujoint bust. and he lost power to his front wheels. if you try to engage it the lights come on on the dash but when your driving you have no power to the front wheels, and there is a clunking almost like some gears are not lining up.

any ideas of were to start?

thanks