No Audio Sound

Hello to all,

I've had my Alienware X51 R2 for about 2 years without any problem, but it just randomly stopped playing sound, It says that there are no "Audio Output Devices Installed" which makes no sense because when I go to my Device Manager all my Audio Devices are there and installed, "they have exclamation marks next to them but they are still installed". I have literally checked over 15 websites for an answer but none of them were able to answer my question, I have no clue what happened other than than that exclamation mark next to them, I just don't know what it means. If anyone could help me with my problem it would be much appreciated :).

PS. I have a Windows 8