Macbook Keyboard Issues

I recently installed a new keyboard into my macbook. Well, not really new, it's used, but it's supposed to work like new. Anyway, now that I've got it installed, the "R" key is acting up. It will random act like it's being held down and pump out tons of r's. But the key is unresponsive to the press. I can't get an "R" by pressing down on the key, it will just pop up at random. I tried replacing the key and scissor mechanism with the one from my old keyboard, and it was no luck. Is this just a faulty keyboard? Or could I have not pressed the ribbon cable down hard enough when installing the keyboard?

PS. I'm typing this on a USB keyboard.