When the RAID controller is not connected to the PCI-e, does DIMM3 appears as populated or not?
We can also recommend you a BIOS update if the motherboard is not running the latest BIOS version.
Try another power supply to discard any power issues.
Try another device on the PCI-e x16 in order to check if the behavior is the same.
When the RAID card is not inserted, DIMM 3 does work indeed.
The system in runnning BpIOS version 59 (60 is the newest) but the 60 udate only fixes a bug regarding USB, according to the changelog.
Another power supply didn't change the situation, and if I put my nvidia graphics card in the same slot, DIMM 3 works.
It is an expected behavior since Raid Controllers are only supported on server platforms.
It should be a compatibility issue, because you tested the video card on the PCI-e and the memory on DIMM 3 works fine.
In addition, Intel® Desktop Boards do not currently support Microsoft Windows Server 2003, 2008, or 2012*. There are no plans for making drivers available for these operating systems.