Did you remove ALL mounting posts then install just the ones required and NO MORE THAN THAT?
It's a common issue we see after folk change boards.
I recently decided to upgrade my computer, I removed an ASUS Sabretooth Z77 motherboard, 16GB of Corsair Vengeance RAM (2x8GB) and an i7 3770K Processor and replaced them with an ASUS PRIME Z270a Motherboard, 16GB G.Skill Trident Z RGB RAM (2x8GB) (F4-3000C15D -16GTZR) and an i7 7700k Processor. I am using the same 1000w PSU, Case and HDD's.
When I try to boot the system everything powers on, the RAM's RGB's, The lights on the motherboard, The fans in the case and on the GPU but i don't get any video output I've tried this with the GPU's DVI connector and have removed the card and tried on the motherboards connector. I have found that when I boot a red CPU warning light flashes momentarily on the motherboard then goes off (I assume this is normal?) and the DRAM warning light comes on and stays on. I press the MemOK! button and the light flashes signifying that the motherboard is trying to make the RAM work but this doesn't work. Before purchasing the components I looked on the G.Skill website and it says the RAM is compatable. I have tried each RAM stick individually and in different slots but no luck. I would have thought that maybe the motherboard was faulty but everything seems to power on fine and the sticks light up as they should.
Any advice would be appreciated, as I said I have checked compatability as best as I could and I have also checked the CPU connector pins.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic