When adding a new gpu to the miner you have to reinstall the drivers I had a similar problem when i added a 3080 and I got the same black screen cuzz I had moved the hdmi cord to the new gpu instead of keeping it to the original card I had in my miner first. So turned off the miner and put the...
I would recommend using trex miner. That's what I use and run the memory tweak in the ethermine file and I get 42hash before I used the memory tweak it was at 35hash. Check out this video to learn how to do it