How do I switch my PC to play sound in mono instead of stereo?

[60spaure]

I think that one of the headphone is broken and that's why you only hear the sound in one ear.

[Myles]

looks like f***ed up your headphones coz for headphones its like surround sound it needs to even out the sound around u so its not all playing in one ear but if u want to play it in both ears either get another pair of headphones OR just play it through the speakers good luck ;D