That's really strange. I have 4 RX 480's (just added a 5th) on the H81 board with 4gb cheapo ram and a G1820 CPU on Windows 10. Runs pretty well. What's your PSU? I'm using a Rosewill Photon 1050, which certainly is nowhere near the best, but it's been running good for quite a while now.
I'm using 16.11.5 driver on all my rigs at the moment and they're running just right. However, I did install other drivers on one of my rigs at some point and if I remember correctly, I had similar issues to what you're talking about. Well, not failing to post, but I was getting crazy BSOD's to the point that I could not login and needed to reinstall Win 10. But Windows 10 will put you at like 16.6 and I just install 16.11.5 and I'm up and running. I wish I had more info to give, but that's been my process and it's been alright so far. At the end of the day, it could be your board. You wouldn't be the first person with a bad H81 board. Just read around.
This was a very old post you replied to.
Most,info,here is out,of,date.
I am locking thread.