Headphone Plug not Working

Okay...I'm really at my wits end.

I just bought a refurbished 1721 and everything works beautifully except one thing: When I plug in the headphones into the headphone jack, the music still comes through the speakers, but not the headphones at all.

This is really wierd. I have had the computer a month and never really needed headphones for playing music CDs until my wife told me to use my headphones one late night.

Has this happened to you? What should I do before sending it back to Dell for a warranty fix?

I am running Windows Vista Premium. i went into the control panel and my sound is working (functioning) properly. I couldn't find anything on headphone jack in the hardware portion of the computer system menu.

Help!!