[SOLVED] No video on boot

[gibmarkney]

I recently built a new computer. I used a Gigabyte Z390 Gaming X mobo, an i5 9600k CPU and 16 GB Corsair Vengance LPX memory.
After assembly, using on-board graphics, everything worked fine. Good graphics, Windows install, ect.
After a few days, I wouldn't have video on boot until I unplugged and reinserted the HDMI cable. Eventually, that stopped working as well.
I then installed a known good video card and had HDMI video again...for a few days.
When I boot I don't get any error beeps(just one short beep) and all the LEDs light to indicate CPU, DRAM, GPU and Boot have completed successfully.
All the fans spool up including the GPU.
I've uninstalled and reinstalled all the components and double checked that everything is seated correctly.
The monitor was checked and works.
I've swapped out the HDMI cable.
Frankly, I'm stumped. I can't think of anything else to try. Everything worked in the beginning. Everything appears to be working now but no video signal.
Any help anyone could give would be greatly appreciated.
Thank you!

 

[dotas1]

Full system specs please. Don't forget make and model of your PSU.

 

[gibmarkney]

OK, sorry.

CPU: i5-9600k @4.6Ghz
Motherboard: Gigabyte Z390 Gaming X
Ram: Corsair Vengance LPX Black 2x8GB @2666
GPU: EVGA GeForce GTX 750ti
SSD: Samsung 960 EVO 256GB M.2 PCIe NVMe, Samsung 860 EVO 1TB 2.5 SATA III
PSU: EVGA Supernova 750 G3 80 Plus Gold
CPU Cooler: Cooler Master Hyper 212 EVO
Case: Nanoxia Deep Silence 5 Rev. B

 

[gibmarkney]

So I've narrowed it down to a couple things...RAM, CMOS or Mobo.

 

[dotas1]

Since the problem started when using integrated graphics, I would bet the mobo is at fault. You can try some things to rule out RAM, such is memtest. If you don't find any errors, you should RMA the motherboard.