truck wont go into gear?

[Silence86]

ok so today i was driving, and im at a red light and as it turns green i give it gas it starts to go and i hear a noise underneath the truck and all of a sudden the truck starts to rev up. i down shift to see if the truck put its self in neutral some how and it still wont go anywhere. i have to pull over with out actually driving it. the transmission goes through all the gears but nothing happens no reverse and no drive. it doesnt down idle when you shift into any of the gears....anyone know whats going on???