[u no who]

I checked control panel/system/hardware/device manager and it shows under "sound, video and game controllers" the one that says "Realtek AC'97 Audio for VIA (R) Audio Controller" has a yellow ! on it. When i double click on it, it says
"This device cannot start. (Code 10)
Click Troubleshoot to start the troubleshooter for this device."

The way i found out that my sound wasn't working was that whenever i tried to play a song, it came up with this error message:
"Windows Media Player cannot play the file because there is a problem with your sound device. There might not be a sound device installed on your computer, it might be in use by another program, or it might not be functioning properly."

I have downloaded a folder that says "Realtek AC'97" but it doesn't seem to help.
If anyone can help i would be greatly appreciated...thanks!
~*u no who*~