Everytime I press the power button, the white power LED comes on for a few seconds, and I hear fan noise then the machine just "clicks" off, almost as if someone removed the power cord abruptly. Needless to say, I didn't remove the power nor was the supply interrupted. I've tried diagnosing the problem by removing external devices one by one, but that made no difference. Also I did all the resets you can think of etc.
"I just had the exact problem on my 2006 MacPro 1,1.
I managed to get it to work. The symptoms where almost identical. It would attempt to start, and then just ""pop"" off again. I took all memory out (except for original ram), my 3 extra hard drives, even the video card, all with the same result.
I ended up taking the ""insides"" apart and thoroughly cleaning every part. I took the video card fan assembly off, cleaned the heatsink and cooling grid, I took the PSU fan apart, cleaned it. I took the front two fans out and cleaned them, as well as the back fan (by the memory). I also cleaned the cooling grid of the cpu. All these items had layers and layers of dust on them, almost like little blankets. While I had it apart I also replaced the CR2032 memory battery, since it is cheap, and I had read that there could be start-up issues if it was old..
After this, it started like a champ, and it was soooo quiet!!!"
Hi There every body, mine from 2011 was dead, some weekends, try to rapair for this time, until i decide to put 3 ATX PSU 20amp in 12v Rail each, one for J1 conector, one for J2 conector and one for J3 Conector the c conecctor use 5vsb 3.3 vsb and PSU-ON and Ground, this mac pros drawn to much current thats the only way to do it satable 3 x 20amp atx PSU, the only thing you miss is the sleep fuction, but you get you $2000 machine back to life, people goes crazy buying used motherboard, Used PSU that have the same problem as original... serach for j1, j2, j3, c pinout take 3 cheap atx psu thats it, J3 goes for hd, pci 6 pin , j2 goes for cpus , j1 goes for pcie, C goes standby power and memory.... waste 1 hour and $60 to bring your mac to life again, you can takeit to apple support they dont get with failure and take your money, here in my countre apple service take from me a video card replacement hd 2900, they say they replaced psu to, i spend more than $600 for nothing, google you will see tons of people having the same problem, and buying on ebay a used PSU it wont work they all have se same problem in short time you will get failure again, is a PSU problem....
"I've got the same problem (early 2008 Mac Pro 8 core 2.8ghz). It boots up if the power cable has been removed for sometime, and runs fine. The diagnostic led's on the logic board do not indicate any problem, but for a few weeks now I have found the computer off after leaving it sleeping over night. This seemed to happen more often, and it would take longer for the chimes to sound after turning it on. I've ordered a psu, so fingers crossed :-)
Update
I fitted a replacement power supply a few days and it has fixed the problem. So I would say that if you have the same issues as Hitcher, it's the power supply."
"I had the same problem too. I operate a Mac Pro Early 2006, but it just can't start up after a long sleep. When I pressed the power button, it seems starting but then just buff off. I've taken all hdds and rams and let the machine running with just os Hd and it seems to be going. I've tried installing the unplug hardware and seems to be working. Another option i normally tried also, which helped to me due with start up issue is a preRam reset by, cmmd, opt together with P and R key, all pressed down after you hear the first chime, and still pressing it till you hear the second chime then released the keys.
But I think i might be agree with dxhole, commenting on the power supply. It could be the source of the problem.
Hope to hear any further comments on this folks.."
