Upgraded but issues

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I just upgraded my gpu from a 1050 ti to a 3070. In doing so I also had to upgrade my psu, which I then installed a 850w, that is to my knowledge installed correctly. I’m rather new at pc building, keep this in mind. My computer turns on and everything lights up, but my monitor is black, also the USB ports on the rear of my pc dont seem to be working. Finally I cannot turn the pc off using the button on the front, I have to use the button located on the rear.
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