When folk replace the motherboard they usually leave all the standoffs in the case. Motherboards can require more or less of these and an extra can short the backside of the motherboard. This happens too often so it's my first guess.
Besides that, you should pull out the motherboard and put it on cardboard and do an outside the case build with the fewest parts you can to see if it works. Only then you proceed to the case.
Hi everyone. I just got a new motherboard, gigabyte ab350m gaming 3, a cpu, ryzen 2600 and a new ram G.SKILL F4-2666C19S-8GNT 8GB DDR4 2666MHZ VALUE. After everything was setup, I powered on the computer and everything lit up, but no beeps or boot from the motherboard. I have some thoughts of why this could happen, first the Ram is not on the list of the compatible rams of the motherboard and secondly I'm not sure if the bios is updated for second gen ryzen CPUs. Please tell me your thoughts about that.