may be the sound setting is changed, go to control panel and sound properties tick all the properties settings, then automatically sound come,else install the sound card driver.
Are your speakers correctly plugged into the computer and possibly a power supply? Is the volume turned up? Do you have the drivers for the sound card installed?
Make sure that speaker or headset is properly connected to the computer, if not you probably need to install a sound card or install a software for the sound card.