Sound goes from a computer's sound card to the speakers. Disruption to any of these components, including the cables, can cause a computer's sound to malfunction. If the computer does not have an integrated sound card, it may have come loose. Alternately, the sound drivers may need to be updated.
To narrow down where the fault is, computer owners can plug a set of standard headphones into the speaker jack in the rear of the computer. If sound is audible through the headphones, the fault is in the speakers. If it is still not audible, the fault is with the sound card. Purchasing and installing a separate sound card should restore the sound.