What happened to my sound???

I've checked everything! My computer is all plugged in, (plus if it wasn't i wouldn't hear anything at ALL) And I went on options and defaulted it twice. My sound is gone!

When I'm playing a gun game, I cannot hear bullets. I cannot hear footsteps. When on knife I cannot hear the knife thudding against the wall. When i get a kill, a very bad voice says "hahahaha" or yells "Headshot" but mostly the HaHaHa is annoying.

I've had this happen before. It usually goes away. BUT IT HASN'T GONE AWAY AND ITS BEEN ALMOST AN HOUR!!! And I tried reloading the game twice. Whats wrong with my sound?