Faulty mac pro
Mac pro 4.1 flashed to 5.1 firmware. Computers start normal, seems to work normal but no chime and no boot and no display out. I try replace gpu, hard drives and memory ram but same issue. After many hours and plenty restarts finally boot one time for few minutes, i manage to post in mac os high Sierra and in ''about mac'' , showing only one cpu running, instead of two ... Is Mac pro 4.1 from 2009 with intel xeon W3520 - 2.80Ghz, is 2x 4gb ddr3 ram and bios seems to be flashed to 5.1 firmware. Trying to check other specs mac just restarted and never post back again !
In the end i swap cpu tray from another Mac pro 4.1 but with only one cpu and Mac pro boot and work absolutly perfect without any issue. Conclusion is cpu tray can be faulty and must be replaced or one of cpu is not working ok and must be replaced ...