I have a problem - I installed mac os high sierra on mac pro 5.1 2x4 cor. After that I dowlanded macos-Mojave and ran the installation with a firmware upgrade. I turned off the computer, installed the rx 570 video card, turned on the computer with the button pressed, until it made a sound, but the screen remained off, after the computer turned off. I turned on the computer again but the video signal didn't appear .I repeated the procedure with original video card but nothing has changed.
it crashed in the firmware upgrade process.
Now I don't know what to do.