I used to hear some programs on my labtop,some times I use headset,suddenly my speakers don't work any more,I can hear only through headphones,how I could hear from speakers again?

It's hard to say. The way a headphone jack functions is when you insert the plug it interrupts the connection to the speakers by moving a spring like clip out of the way and causing the common connection to the speakers to cut out. That way when you remove the plug the springy clip returns to its original position creating the connection to the speakers once again. If the clip is weak and doesn't return, or is broken off (made in china) the speakers cannot function. Are you sure your speakers are not muted in your settings?