Double click the speaker icon in the lower right hand of the desktop, this will bring up the mixer, or single click to bring up the volume control. Laptops: see below, third paragraph.
Check the setting of the mixer or volume control.
But in case the volume is missing, corrupted, or the audio is otherwise non-functional:
you check whichever audio was installed:
click start, click control panel, click add remove programs, look at the list...
which audio software is shown on the list? delete it, restart the computer.
now visit the motherboard manufacturer or computer manufacturer's website
look up your computer drivers by model number
download the latest audio drivers, save on the desktop...
turn the antivirus off,
if you have multiple security programs installed, turn them all off
(your driver may not install if security systems are turned on)
now load your new audio driver, restart, turn the antivirus back on.
Laptops: Your volume controls may be built into the keyboard. (varies according to make and model number)
OR: your volume control may be a knob, located near the headphone jack.
Download the entire manual for your computer model from the manufacturer's website.
The manual will show you where all the keyboard audio or wireless ethernet controls are located.
But besides the manufacturer keyboard controls, you will still have software controls, as above. (first paragraph)
So if "either one of these volume controls is turned to "zero" you will have no sound. If the Mixer is turned to zero, or muted, you will have no sound.