My Mac Pro 2010, running Sierra 10.12.6, boots but the screen only stays on 2 seconds and goes to black. I can push the power button on the screen monitor off and on and it comes back on for 1 second then goes to black. Every time I push off and on it comes on then goes off.
GPU was changed because the old GPU was putting thin colored vertical lines on the screen and would not stay on but 1 second. The new GPU did away with the lines, but the screen will not stay on. The computer works fine, I can power the monitor off and on and see the screen for 1 second. The images on screen during that second are correct. I can see the cursor move, upload the internet, but only for 1 second.
PRAM reset does not work, SMC reset does not work. Changed to a different screen with different cables and it does the same thing. Is this still a GPU problem or is there something else that turns on/off the screen? Turned off screen saver, sleep mode, no change.