Try to buy a replacement to fix from here: http://www.ownta.com/canon-ixus-500-digital-camera-repairing-lcd-display-screen-replacement.html
But I am weird why the Horizontal line on all your pic's/video's, it only appares when you view on your camera, not appears when you download the picture to your PC, right ? if yes, then, it's your camera lcd problem.
Kare
August 2009