Why do I get occasional colored lines across half the screen?

I thought at first that my hard drive had crashed because I tried to start up the machine and it made it to the apple on the screen, but then no further. I tried restarting a couple of times and it was no go. Then I tried again after a couple of weeks and it booted up just fine. I have even upgraded to Leopard since then and it's doing fine. But every once in a while, I get what looks like a bunch of colored lines that completely obscure part of the display - usually the lower half of the screen. If I wiggle the screen, I can make it go away. Perhaps this is unconnected to the earlier failure to boot, I don't know. I have a suspicion that the cable that connects the laptop's display is malfunctioning, but I thought I would ask the experts and seek the recommended repair.