Gamecube Short?

I am having a recurring problem with my Nintendo Gamecube. Sometimes, when I plug in more than one controller, it shorts the game out and turns the power off. I am using official Gamecube controllers. They all seem to work fine plugged in alone in the 1st player slot. I went and bought another gamecube, AND wouldn't you know, it is doing the same thing now (after about 1 week). EB Games and Game XChange are clueless. They will replace my game, but that doesn't seem like it will fix my problem. Anyone have any ideas???????????

Gene