Computer speaker problem! Sound just stopped. (details)?

I was listening to music, (at medium volume, as always) and all usudden the sound stopped. No crackling, No static, both speakers, as if i hit mute. (which I did not) Checked volume control, but nothing was changed. So I plugged a headset in through them, and sound was coming out on the headset, but still nothing on the speakers. So then plugged the speakers system into another computer, still nothing, and still sound only comes out of the portable headset speakers. Any ideas on what had happened. Are the speakers blown?