Hi everyone, I am posting this because I was affected by the "No HDMI connection" issue and I found a fix for it that nobody else mentioned (at least to my knowledge). I followed two leads when I figured it out. First the fact that I got the error only after I restarted my PC and second, a lot of people mentioned that its to do with power delivery through the USB slot. Anyway to the point:
Fix: It appears some motherboards including mine (ASUS Z97 PRO GAMER) selectively turns on USB slots during POST stage. It only does it for the keyboard and mouse controllers. I think that when the system boots the driver for the GPU loads before the drivers for the USB Hubs meaning when the GPU tries to figure out what is connected to it and it can't because Rift doesn't have power at that point. To fix that I have adjusted the settings in the BIOS to force the motherboard to power on all USB slots during POST stage.
I have tested it over the course of the day, turning my PC off and on again couple of times and so far the issue is completely gone. If something changes I'll post it here but I thought it would be good to share that as it could possibly fix your issue too. It's something to be picked up by Oculus'es support staff as well.
Where in the BIOS did you find these settings? For me I get this error maybe once every 5 or 6 reboots. And if it happens the only solution is to reboot and hope it doesn't happen the next time.
@korgen63 You need to enable advanced mode while you are in the bios, then go to the Boot tab and under usb select full initialization from the drop down box, then save and restart your pc.
I have an Asus Z170 Sabertooth Mark I. I could not find an option that appeared to do this. In my case, I corrected the HDMI connection problem by removing the foam cushion from the headset and re-seating the HDMI connection on the Rift itself.