I have a Compaq presario cq50 115nr notebook PC and for some reason after I downloaded an important update (it was an automatic update), the sound has a red x over it and no sounds will come out. When I right click on it, it says the device is enable but there is no audio devices installed.

Do I have to reinstall the driver for it or something? If so, where do I get it?

Yep, seems your sound driver has gone for a burton.
Head over to HP's site and grab the correct driver for your model.