quoting:
Unplug speakers and plug headphone into the now empty jack.
Don't put the volume too high though. You could fry your headphones.
It is probably the "line out" jack you're using, it's not really meant for
headphones. Line out puts out a "flat" signal for an external recorder, or
processor that needs a clean, unedited signal. Computers generally don't
have headphone jacks. Sometimes you get lucky and you have a set of
speakers that has a built-in headphone jack. cd drives usually have them,
but they are nothing but a line out with a volume, but better than nothing,
I guess. You can use the speaker jack, but just be careful not to fry your
headphones. Sometimes, though headphones will have a built-in volume
slider, you can turn this slider way down so you can safely use the speaker
jack.