What's Wrong With My Xbox Cords?

I, like so many other people, just experienced the Red Lights of Death on my Xbox. I called Microsoft, had the box sent in to be repaired, and they ended up just sending me a new one back. All my cords were left in the exact same spot they were the day I unplugged the Xbox to send away. Now, when I plugged everything back in, the power cord worked just fine, but the cord with the red/yellow/white plug-ins is acting up. I can hear the sound when I turn the Xbox on ( you know, that trademark "whoosh" sound that occurs every time you start up your system) but no visual whatsoever. Obviously everything's plugged securely into the Xbox, but now out of nowhere the visual won't work. I can't find any logical reason for this. Please help!