Dual TitanV's - No video signal on boot!

Trying to troubleshoot a no video signal issue. Running Ubuntu mate 18.04 LTS on a dual boot Ubuntu-Windows machine. (Asus X399 Extreme mobo)
When trying to boot this evening was getting no video signal.
I have dual Titan Volta GPU’s and tried switching the HDMI cable to the 2nd GPU. No difference.
Also tried clearing CMOS.
Has been working fine for a year or so. Never experienced this before.

Not getting any error messages on the motherboard on boot.
I know my monitor is fine because I can plug my laptop into the 2nd HDMI input. Both GPUs are getting power as I see the fan spinning.

Is it possible either a recent software and or driver update has hijacked the video out signal?

Is there some keyboard combination I can try on boot?
Any feedback welcome!

Issue resolved.

Tried booting from Live USB using Esc and F12 key options.

Was about to start disassembling, pulling video cards, etc but tried booting once more.
This time at least was seeing a post error on my mobo.
Plugged in my hdmi cable and hooray, was seeing the American Megatrends BIOS screen.

After adjusting BIOS and booting into Ubuntu rechecked my video driver settings and could see that the X.org driver was selected instead of Nvidia 415
This could be a clue as to what caused my problem though not clear why this would result in NO video signal at all.
Anyone aware of this issue with X.org Nouveau drivers?