How to change the output headphone jack on a vista pc?

Recently I just bought some nice shiny new headphones with attached mic, so imagine my disappointment when after a while the rear headphone jack to my computer suddenly stopped working and no matter what i plug into the jack, may it be speakers or my new headphones, no sound will come out of it. Being reasonably computer literate I checked it out in control panel to find the 'headphones' option was grayed saying they are not plugged in, even if they are, and stating that the sound is selected to play out of the front headphone jack which works perfectly fine if my headphones are plugged into it. Now I know I could just plug it in the front slot but then i couldn't use my mic at the same time as the only microphone input is at the back and the lead cant stretch that far. So basically what im asking is do you know how to change the vista settings so that the sound will played out of the back headphone jack instead of the front....