Ok, first have you tried using a different program like iTunes ?
Can you still hear system noises (like the windows sound when the computer boots) ? This will tell you that al is well with your speakers and the sound card.
Have you tried installing a newer version of the sound card driver ?

Also have you checked the connection between the CD player and the sound card ? their is a digital cable (just a little teeny weenie one necessary for direct digital data transfer).

Hope this helps some, if we can at least rule out a few major things than perhaps we can find put 1) what the problem is and 2) a cheep way to fix it !