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The component cables for the both old and the slim version of xbox360 are the same, they are both interchangeable.
As for getting no sound, make sure you plug in the cables correctly. Watch out for the red colour cable, since one is for audio and the other one is part of the video signal. If you line it up flat, the one beside the white cable is the audio.
Try that out and see if it works for you 
This should be the actual standard component cables, the one before had an option to switch between composite/component option with the extra yellow plug.
Anyways, hopefully you would get your problem resolved in-store. It's a lot easier to diagnostic a problem directly than reading it on the forums.
