Hello everyone. If possible, I would like to continue this topic because I have the same issue. I have thoroughly measured the power sequence, and everything seems fine, yet it exhibits the same symptoms as the machine in the initial post.
What I have as additional information is that there is no communication on the LPC lines. The PCH reads part of the BIOS from the flash IC. As far as I know, the crystals are working (25MHz crystal vs. 20MHz oscilloscope).
The PCH SUS_CLK# clock signal is present.
What could be worth investigating?...