Buildapc

I recently built a computer for someone. It was just for general use, not gaming or anything, so I went with fairly simple specs. Because they wanted an insanely quiet computer, I went with an NHD15S. The problem is that cooler causes flexing in the motherboard that makes the CPU not make contact with the socket. Is there a not overly janky way that I could fix that without getting a smaller cooler? I know flexing is the issue because it works for a while with the big cooler, but eventually won't boot after being shut down, or crashes in weird ways and then won't boot, and the mobo lights always show a CPU and dram light. The box cooler has no issues, but is louder under load.

Edit: it does boot with the large cooler if the system is on it's side. I followed the mounting instructions carefully.

Edit 2: Solved. I was overtightening.