Random sound disappearances

Hi,

I have a Envy Spectre 14" with Win 8.0. For the last month or so I have sound disappearing (totally) at random times. Rebooting has generally solved the problem...but that can be a pain if I'm in the middle of a lot of projects. It was working this morn....closed the lid...opened it 30 min later and NO sound.

Hope someone can help me.

Thanks!