Custom Build PC, Windows Boots Inconsistently/Intermittent Video Signal On Boot

Question

My friend and I built a new machine together a few months. The rig has the following specs:

Motherboard: ASROCK Fatal1ty X99M Killer
CPU: Intel i7
RAM: 16GB, 2x 8GB DDR4 Crucial Ballistix Sport 2400 MHz
HDD: 256GB Boot drive, SanDisk 
OS: Windows 8.1
GPU: 2x Nvidia GTX 980 in SLI
PSU: 1200w
Extra: Blu-ray player

The system was built in December. It has operated fine since then. A few weeks back, it was updated to Windows 10. Around this time the system began failing to boot properly. When booting the system typically there is no signal to the monitor; hard rebooting generally will bring up the system with the Windows Automatic Repair utility, from which you can run tests and the like. In other words, trying a regular boot will fail with no signal to the monitor, and rebooting will bring up a signal with the Automatic Repair utility shown.

Using the Automatic Repair utility I've done a System Restore to return to Windows 8.1; this has not helped things. Again from the Automatic Repair utility, I've used the command prompt utility to run:

Bootrec /fixmbr
Bootrec /fixboot

Using the Automatic Repair utility I can boot into Safe Mode including with Network Options; using this I have performed OS updates as well as installing the latest driver for the graphics card. I've run my Anti-Virus software to no avail. None of these changes seem to help.

I've tried a different monitor so I know that isn't the issue. The monitor is connected via a DVI connection; I've tried HDMI also. I've pulled one, and then the other card to test them and that appears to have not impact. I've pulled both cards and replaced them with an Nvidia GTX 770 (I believe); again, no impact. Ostensibly that might not help if it's an issue with an Nvidia driver.

Using the Automatic Recovery I just finished a clean OS install, to Windows 8.1 with all updates including latest Nvidia driver. After the updates were finished, I rebooted and again nothing; I saw the POST and then after that there was no signal. At this point I'm feeling like there is some type of hardware failure; such as the motherboard. I've been trying to read through what appear to be related articles but nothing I try seems to help; and suggestions/questions are appreciated.

Update: I've pulled both of the graphics cards and put them into another system in SLI; everything works fine which encourages me to believe this isn't an issue with the cards.