yeah it may sound really stupid but make sure your speakers are connected if you use them.i went two months not knowing why my computer wouldn't play soudns when i had to take my keyboard out since it had broken and stupily found that my speakers plug had fallen out of the computer :(lol
i went on youtube guess what i heard, SOUND,
Plug-In your speakers.
I had a similiar problem before, I could only hear some sounds, like in game I could hear sound effects but not music. Turned out I had my speakers plugged in to the wrong port, so make sure there in the right ports.