I've had an odd issue with my Maximus VI Hero since the day I've had it, about about 8 months ago:
Basically, changing any BIOS settings can cause it to go into a loop during POST, showing 00 Q-code on board, and a blank/suspended monitor. It repeatedly reboots like this every 30 seconds as I can hear the fans spin up and down and the system must be forced to power off. Once this issue occurs, it's impossible to boot the machine until the BIOS is re-flashed, and this seems to fix it most of the time. It doesn't matter what BIOS setting I change, it can be anything from a BIOS version update, changing the RAM clocks, disabling on-board sound, to changing the boot order. But it doesn't happen every time a change is made. And once the machine is able to boot, it always boots; it reboots, it cold boots, and just seems to run 100% stable, slightly overclocked, uptime for weeks and months straight, no crashing. The issue ONLY occurs when changing BIOS settings and updating BIOS versions.
For example: attached is no more than a CPU, PSU, a single stick of RAM, and a monitor via onboard HDMI. From a clean BIOS flash, I went into the setup and changed only the boot order and restarted. I did this five times, four of those times the board would not POST and I had to force it off and re-flash it using the USB BIOS flashback function. I did the same test with disabling/enabling onboard sound with the same results. Going in and changing a whole bunch of settings causes the same results and frequency to fail.
I was very lucky to manage to have changed all the settings I needed on v 1301 in one shot and boot properly, so I didn't dare touch the BIOS for months after that. I recently installed the new BIOS v 1402, and I can't say that the issue is gone, but it seems to happen much less frequently. So, I'm guessing this is a known issue with a percentage of these boards caused by a faulty or glitchy BIOS or something closely related to the BIOS. There seems to be a few similar problems reported here, but I'm not sure if anyone has done as thorough testing as I have.
Here are the various hardware configurations I've setup with this board, I'll leave out the many hardware components that I had eliminated from my testing. This issue persisted regardless of my hardware configuration:
CPU: (only one CPU was tested, but it did work flawlessly on another gigabyte board I was able to get my hands on)
Core i7 4770k
BIOS Versions:
nearly every version prior to 1301, and now recently version 1402.
HSF:
Cooler Master Hyper 212+
Corsair H80i
PSU:
Enermax Infinity 720w
Antec HCP-1300 Platinum
RAM:
1x (2GB) Corsair Dominator TR3X6G1600C8D 1600MHz
1x (8GB) Corsair Vengeance Pro Series CMY16GX3M2A1866C9 1866MHz
Chassis:
Lian-Li PC 60FNXW
Fractal Design Define R4
