Audio Drivers not working at all.

Hi everyone,
I switched on my computer this morning realizing there was no sound working. The little icon in the bottom right corner in the tray has a red "X" over it. When I go into device manager my Sound, Video and Game controllers is missing from the drop down list. There are two drivers on the list which have a yellow exclamation mark over it and whenever I try to update the drivers it doesn't work. I'm running Windows 7 64bit. I'm working on an important project, any suggestions on what I should do?