When do headphones work in the versa jack?

I didn't know what all the sound card jacks did on my PC, so I looked in my manual and now I see that, since my two audio out ports are taken up by speakers and a subwoofer, I can use the free versa jack for my headphones. I plugged them in, but there is no sound. How do I use the headphones? Yes, there is another headphone jack in the front of the PC which does work, but it's a headset I'm using, and the two plugs (one for headphones, one for the speaker part) are close together, so I can only use the jacks that are next to the mic jack.