Audio problems on Windows 7?

I always have my headphones plugged into my computer but just now, out of no where the sound started coming through the speakers even with the headphones plugged in. I put in a different pair of headphones, thinking there was maybe something wrong with the ones I had, but the other ones didn't change anything either. I'm not sure how to fix it, or what's even wrong, I was using my headphones only a few horus ago but now the sound won't come through them. Any ideas on whats wrong?