Sound on my Macbook not working?

I had this problem a month or so ago and tried everything such as updating the software, putting headphones in and out a few times, restarting my computer and resetting the PRAM and SMC. Nothing worked. I then didn't use my mac for about a week. When I turned it on after that it made the restart sound and the sound was working fine. But now it once again isn't working. Any ideas on how to fix this problem? It isn't on mute.