Real quick, just to completely understand
you are using a LCD TV/Monitor as your computer display, and you have a wide blue plug that u are connecting from you computer to your display?
if yes, the blue plug only relays video, so there is going to be a plug from your computer called "audio out." make a connection between the Audio Out from your computer to the Audio In on your TV! This plug should look identical to a head phone jack that you can find on a ipod or something similar. you will need this cable (cord really, i think of cables when i think of Large cords) that has 2 male ends (Male end plugs into a female end)
Computer <-------> TV Speekers
Reference:
Male End: -
Female End: < and >
Cord: ------
Hope that Does the trick!