Is my GPU the problem?

So, i have installed a GPU, my first GPU actually. I followed instruction, tutorials and everything there is to make sure i install correctly. When i boot it up the mouse is slower, the whole PC is slower actually and after some time the screen kinda of freezes and everything kinda shatters. Reminds me of when pixels die. Then it slowly fades off in to a black screen. It doesn't even let me open the AMD to install the drivers, it tells me that i need to connect a different monitor or something like that. I tried to bypass this by going to the hardware from windows it self and searching the drivers in C:\AMD but it didn't install anything. If i try to connect the monitor to the mother board instead of the GPU i don't get a video at all. When i get the GPU out and boot up, the PC works normally like it always did. I tryied different cables, i don't think it's the issue here, but i'm honestly not even sure at this point. Is my GPU broken and I should return it? Maybe it's a problem with the mother board? Idk pls help me, really don't know what else to do.