this is my own experience to solve the non start up problem to a Mac Pro 2010, I write down almost all possibilities which the problem could come from, and the solutions:
here I've reveiced a Mac Pro 2010 mono processeur 2,4 quad original, it did not start up at first power on, commun after longtime shipment, I replace the logicboard batterie, then I tried with 5770, it powers on and entered the system with no problem, but when I change to high performance video card it wont start up, and it gave just two quick clicks from the psu place at first power on after card changed, then stop, and wont give a sign of life after.
this seems at least psu or logic board has problem, because it looks like lacking the power to supply new card, so I connect to another psu external, and it doesn't solve the problem, then I pull out the ram, the video card, the hdd, then it goes on normally,
so psu seems fine, I turn to my head to the video cards, I tried gtx 680 and r9 280 on another mp, don't have problems to start up, so the video cards are just fine
I really don't want to replace my logicboard to waste my 30 min, so i changed the cpu tray with worked one, it did help anything
so I start to thing about the power management on the bold system, so I decide to upgrade the logicboard rom with high Sierra installation, after the upgrade the mp start up first with 5770, then I changed with the first video card 680, it starts up and enter to mojave preinstalled,
woofooooo, it's finally come back to life, to make sure I turn on the cpu burning test, and it still on fine after half hour test, so I thought it is ok now, before close the case, I decide to test with second video card rç 280, it did again the psu two clicks thing, and ... dead again ....... wtf!!!
ok need I have to start over ? it left me the last part doesn't change yet, but I don't think it comes from logicboard, it is rare that it starts up with one gpu but not with another one, especially I've upgrade the mp to newest rom, so I think I maybe the cable problem, so I changed all video cable, this time the mp starts up with all video cards, wow, so finally it's one of the video power cables having problem, I did realized that because 5770 use only one cable, when I use two cables to power the new gpus, the second power cable has issue, I replace the second power cable, now the mp has its life really back on
so it is the end of story, if your mp doesn't power on, hope this experience could help, have fun.
here I've reveiced a Mac Pro 2010 mono processeur 2,4 quad original, it did not start up at first power on, commun after longtime shipment, I replace the logicboard batterie, then I tried with 5770, it powers on and entered the system with no problem, but when I change to high performance video card it wont start up, and it gave just two quick clicks from the psu place at first power on after card changed, then stop, and wont give a sign of life after.
this seems at least psu or logic board has problem, because it looks like lacking the power to supply new card, so I connect to another psu external, and it doesn't solve the problem, then I pull out the ram, the video card, the hdd, then it goes on normally,
so psu seems fine, I turn to my head to the video cards, I tried gtx 680 and r9 280 on another mp, don't have problems to start up, so the video cards are just fine
I really don't want to replace my logicboard to waste my 30 min, so i changed the cpu tray with worked one, it did help anything
so I start to thing about the power management on the bold system, so I decide to upgrade the logicboard rom with high Sierra installation, after the upgrade the mp start up first with 5770, then I changed with the first video card 680, it starts up and enter to mojave preinstalled,
woofooooo, it's finally come back to life, to make sure I turn on the cpu burning test, and it still on fine after half hour test, so I thought it is ok now, before close the case, I decide to test with second video card rç 280, it did again the psu two clicks thing, and ... dead again ....... wtf!!!
ok need I have to start over ? it left me the last part doesn't change yet, but I don't think it comes from logicboard, it is rare that it starts up with one gpu but not with another one, especially I've upgrade the mp to newest rom, so I think I maybe the cable problem, so I changed all video cable, this time the mp starts up with all video cards, wow, so finally it's one of the video power cables having problem, I did realized that because 5770 use only one cable, when I use two cables to power the new gpus, the second power cable has issue, I replace the second power cable, now the mp has its life really back on
so it is the end of story, if your mp doesn't power on, hope this experience could help, have fun.