Repetitive Restart - Mac Pro Early 2008/3.1/El Capitan

[jim harper]

Not sure if this is a software or hardware problem. I believe I've eliminated the drives and memory as problems, and in fact now I'm using one of the drives to post this, on a Mac Pro Early 2009. All the drives I used on the problem machine work fine on this one.

I have tried all the usual troubleshooting commands and none worked. Tried resetting SMC and PRAM. I can't use a startup disk and can't re-install the OS because it won't reach the Desktop when attempting to boot. Nothing works.

When the power button is pushed, the startup chime is normal. Then the apple shows and the progress bar proceeds. Everything looks like a standard startup. Then when the progress bar reaches about 2/3 finished, the screen goes black, and it goes through the startup process again. This continues over and over non-stop. The only way to prevent the continual restart is to hold the power button and do a shut-down.

The only PCIe card is the display card. Since the startup process shows on the monitor, I presume that card is okay. So, my question is: Where in the CPU would a problem be that would allow the OS to attempt a restart and fail before reaching the point where the Desktop appears.

Thanks for any help.

 

[chscag]

My guess is that you have a flaky power supply - either failing or getting ready to fail. Common problem with a Mac Pro of that age. Could also be something else, but I would start with the Power Supply.

 

[Quinten]

One thing you can also try is putting the Video card from the 2009 machine in the 2008 machine to rule out that it is not a video card issue