when i try and play something in windows media player or nething i get this error

"You either do not have a sound card installed on your computer or it is not functioning properly. If you do not have a sound card installed, you must install one before you can listen to audio in a digital media file. If you do have a sound card installed, refer to its documentation to troubleshoot the problem.

Error ID = 0x80040256, Remedy ID = 0x00000000"

how can I fix this?