Or you don't have speakers.
My money's on you having your speaker jackplug in the wrong hole at the back of the box. Modern computers have sound cards as standard. Very different in my day....why, way back in....ooh, 2000 I think it was, you had to buy a sound card separately, and if you didn't know how to install it you took it to a computer shop where a spotty, supercilious young git, hardly old enough to shave, would throw a disgusted look, then patronise and humiliate you.
It's a terrible thing, killin' a man.