I have a MacPro 3.1 and the screen continues to go black and the fan starts blowing at high speed.
I excluded that it was my operating system by running Clonezilla and trying to clone the hard drive. During the clone, he finally presented the same symptoms.
I was able to clone the hard drive on another machine without any problem.
I also plugged in, only a stick of RAM while trying to clone the hard drive and got the same results, so that leaves the logic board, the PSU and the processors.
I'm trying to follow the path of the CPU, but I can not dispel the heat sinks for the repasts.
I've loosened the 4 screws on the processor A heatsink and I still can not remove it from the processor, I hear a lot of crunches, but that does not dissipate.