I have just finished building a HTPC and have ran into this exact same problem, even with the problem with the computer not booting if there are RAM sticks in slots 1 and 3. But, it is an even worseproblem for me because I only have 6GB in the computer and 4.6GB are being hardware reserved, so it is too slow to use. I temporarily swapped in 16GB of RAM from my main computer but even then there was still 8.8GB of RAM hardware reserved. It works well with the 16GB of ram but I need it to work with the 6GB because I need the 16GB from my main computer. It has been a while since anything was last posted on this topic so I presume that you have gotten further with fixing the problem, could you tell me how you fixed it, if you did?
HTPC specs:
CPU: AMD A8-6500
Motherboard: MSI MS-7906
GPU: AMD Radeon R7 200
PSU: Corsair CX500
Storage: WD 1TB HDD