This is usually one of a few things.
1. The motherboard is shorted out by improper mounting. Take the board out, put it on cardboard and do a power up test there. I use the box the board came it. This is well discussed so ask more if you don't know how to google or how.
2. The CPU is not seated. Remove the CPU and test without the CPU.
3. There is a dead part. If items 1 and 2 don't show signs of life, then get the motherboard RMAd.
More at https://www.google.com/search?q=gigabyte+ab350m-ds3h+won%27t+power+up+site:forum.gigabyte.us
When ever I try to power on my pc, it refuses to do it if the 8pin power for the CPU is plugged in. I've tried plugging every thing in indevidualy and I know it can power on without issue. I replaced the power and now know it's the mobo 8pin female connector that's the problem. Ever thing looks in order when I inspected it. Does any one have an idea of what the problem is.
Motherboard: gigabyte ab350m-ds3h
Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic