I used to get this with earlier versions of Ubuntu (which is based on Debian). It turned out to be just that not all BIOS manufacturers had properly implemented the ACPI power management.
PBLK was some structure in the BIOS and Ubuntu expected it to be correctly formatted.
The only downside for me was that the machine didn't power off completely on its own. It had to be manually cycled when the final shutdown message appeared from the kernel.
I found that, short of recoding a chunk of the Linux distro, there was no way around it.
I've long since tossed out both that motherboard and the early Ubuntu (so I don't actually know if a later Debian would fix it) and no longer have the problem. You might want to consider those possibilities if it worries you.