What to do to solve this laptop problem?

Okay, I’m not really a tech savvy person so I don’t know what to do.
Any help would be much appreciated :)
I have Windows Vista on my laptop, and all of a sudden I turned it on a couple of days ago and found that it’s sound system isn’t working.
The volume control icon comes up with an error saying “There are no active mixer devices available” when I click on it.
It’s also not playing any videos or media files either, what’s wrong and what should I do?