Why does my in game sound sometimes not work?

I would say 95% of the time I would say that my sound while playing league works just fine, but that 5% of the time the game is just silent. can not hear in game actions or pings, just silence. I don't touch any of my volume toys or mess around with anything that would cause this to happen, it just seems to happen randomly.

When I open up my volume mixer league of legends doesn't even show up so I can't even fix it because it never showed up and changing the volume settings in game does nothing.

Any summoner worth their 2 cents knows that playing without sound while you are used to playing with sound is very frustrating and I have missed numerous ganks and important pings because of this.

Has anyone else experienced this or know what might be going on and if you do how might I prevent/fix this. Any help or advice would be greatly appreciated.

P.S. I play on a dell toaster laptop and while it isn't as quality a pc as most others I doubt that this is the reason for the silence, but I am putting this here just in case this information is useful.