Lost of sound on my acer computer

Check in Device Manager to see if the sound card chipset is still recognized. If so, try installing the drivers. Otherwise, it is a hardware issue, try cleaning the headphone jack, there might be something shorting out the jack inside, so Jack sensing turns off the speakers.
 
Also go to Sound in Control Panel.
Open the Properties of Speakers and check the Level tab.
Make sure the output is not 0 (zero).