Why is my Xbox screen flickering?

I was going through old stuff today and found my original Xbox. I played it for a couple of hours then turned it off. The next day I turned it on and it was working, but then I plugged in my controller and the screen started to flicker. It would be normal then the screen would get dimmer then black and would just flicker between that. Only time the screen will flicker is when I wiggle the controller port, but the screen won’t go back to normal when I unplug the controller. If anybody knows anything please help me??