The standard color for audio out is green, so check it's connected to a green plug(not that all are, but most...) Be sure the speakers are powered. Unless they don't have an amp at all, they require power to get any audio. Unfortunetly they can't simply bypass the amps.
If it still doesn't work, try some speakers or headphones you know work. Try the different ports and see what happenes. You can't hurt anything by trying them all, just be sure the volume isn't too loud so you're not blasted away when you do find the correct one
