you say there is no signal in your display, I'd make sur your pcie slot of your gpu is powered:  I would connect a x6pcie (from the psu) on the connector named " POWER_CUT1 ", we can see it on the 4th&6th photos  which should be what powers the first pcie gpu slot (where is your gpu)

I would connect your display hdmi to your gpu hdmi connector

the red light seems to be on the (msata?) disk ?
maybe you can try to remove and re seat it again, or remove this disk and boot without it to see if you can access & see the bios, and if the disk is faulty just use another one (sata one, ssd, hdd or even usb stick with os on it)

I never had a riserless motherboard but this is what I would try if I were in your case.