Windows Media Player 9 Series

I have a Dell Dimension L500r computer. When I loaded Windows Media Player 9 series, I get the following message:

"Windows Media Player cannot play the file because there is a problem with your sound device, such as a sound card or sound controller. You may encounter this error message for one of the following reasons:

Your sound device is in use by another program.

Your sound device is not functioning properly.

You do not have a sound device installed on your computer."

It then gives the following information:

Error ID = 0xC00D11BA, Condition ID = 0x00000000

The interesting part of the problem is when I log into AOL, I hear the standard "WELCOME" through the speakers.

Any ideas? Thank you in advance.