Xbox 360 on HD ready TV?

I have a HD ready TV from Sony, its a CRT flatscreen and I have the red,green, and blue inputs on my TV for hd. I connected the hd composite A/V cables to the correct colors and I set the switch to HDTV, so why does my video appear very blurry with black patches and snow, the audio is good. If I switch the switch to TV the video and audio is good.