Screen Blank

I replaced the GPU because the screen was filled with thin colored vertical lines. The new GPU solved that problem, but when it boots, the screen stays on for 1 second and then turns black. I can turn off and then turn on the Screen Monitor Power button and it will display the correct images on screen for only 1 second. I can do this repetitively and sign on to the internet or do anything I can see to do in that 1 second, so the computer is operating correctly. I did the PRAM reset but no results. This is a Pro Mac Tower 2010 OS Sierra 10.12.6.

I replaced the GPU because the screen was filled with thin colored

vertical lines. The new GPU solved that problem, but when it boots, the

screen stays on for 1 second and then turns black. I can turn off and

then turn on the Screen Monitor Power button and it will display the

correct images on screen for only 1 second. I can do this repetitively

and sign on to the internet or do anything I can see to do in that 1

second, so the computer is operating correctly. I did the PRAM reset but

no results. This is a Pro Mac Tower 2010 OS Sierra 10.12.6. I also switched monitors and cables to rule out those possibilities and had the same results of black screen after 1 second of desktop. The computer stays on the entire time, only the ViewSonic screen power button is turned off and then on.