did you plug all the wires in accept the yellow one?

miscs

what do you mean, which ons do i need to plug in?

I decided to splash out yesterday and bought myself a new 32" LCD TV.  At the moment its working great for my 360 but i was just wondering if there was a difference in quality between the HD cable (blue green and red) and the normal tv cable (yellow red and white).  As of yet i have still not managed to get a picture from the hd cable, is there something i could be doing wrong.