Having issues with my new pre-built PC, help!

I just got a Skytech Vision 011 pre-built PC, and I'm having a lot of trouble with it. When I try to play games like Fortnite through the Xbox app, the game freezes, and there's an error related to the game driver. Counter-Strike 2 lags terribly too. I suspect it might be a GPU issue since my GPU usage shows 0% when I boot up. The biggest problem is that my screen keeps flickering non-stop, especially during gaming. I've noticed that the cables below aren't connected to anything except what's going to the motherboard at the bottom. I'm confused and need help because everything looks fine, but the issues make gaming unplayable.