I have a PC based on an ASRock Z97M OC Formula, I5-4690S, MSI GTX 960 & Windows 10 Pro. on the 4th PCIE slot, I also have an Adaptec RAID controller 6805 (with 6 HDDs connected to it, if it matters). 

The system ran fine for a few hours after the installation of the new motherboard (all other components worked fine with other ASRock motherboards until now) until out of nowhere, it refused to boot Windows 10 and started displaying a B2 (most often) or A2 (sometimes) on the lower right corner of the screen.

When I remove the RAID controller, the system boots just fine. When I'm connecting the controller, I can access it (it is a computer of its own that is booting before Windows) and its status is just fine, but after it has booted, everything comes to a stall like I described in the previous paragraph.

I have used this very controller on other ASRock-based systems just fine until now (Z97 Extreme 4) without such a problem.

Do you have an idea on how to resolve this?

Thanks,

Sincerely,

Antoine

I read that motherboards not compatible with a so called "port-multiplier-function" could experience such boot freezes when a RAID controller (or a simple PCI-E SATA expansion card) is attached to them. 

Does that ring a bell to anyone?

Antoine