Had my cambridge audio HDMI cable fail on me today so went and conected my hd sky box with a spare scart lead i had. The normal picture was better with normal stuff ie nash bridges on fx. But hd was worse as i expected. Found the free be sky cable under the stairs and connected it up to the box and the picture was very bad and so was hd content. To me it proved that buying good cables is worth the extra cash, as even my wife noticed the differance. jk
Buying 'good' cables is always worth the extra cash. However buying 'expensive' cables is often a waste of money
Perhaps you should post a photo of the bad picture as the fact that you're saying that your previous cable failed might imply something else is wrong....