Question Troubleshooting GPU installation

N4x

Jan 9, 2021
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I swapped my old gtx 970 and a thunderbolt card to make room for my new rtx 3090.
I put three 8 pin connectors individually sourced on the GPU from my 1,000 watts Corsair gold Power Supply.
But I got no display on my monitor using either hdmi or dp cables.
i then tried to installed my old gpu back to work on the drivers but again I get no connection to the monitor.... any advice or recommendation ?
I tried connecting the monitor to my laptop and it works fine.
Any advice ?