speakers busted?

okay, so i just realized this today and it just started today, but my speakers are busted on my powerbook. when i plug them into an external speaker device using the headphone jack, it works fine, but once i unplug it, the speakers stop working completely. i've turned up the volume all the way and still nothing. can somebody help me out or am i going to have to bring it back to the mac shop and get a replacement? hopefully this can be fixed. thanks for your time.