R5 1600 with Assrock pro 4 ab350 help needed!

Hello! I am having some issues with my new build.

R5 1600 Assrock pro4 ab350 1080 windforce gigabyte M.2 sata 6 GB SSD Wd 3.5 sata 111

My computer wouldn't post with my gigabyte 1080 in the pcie 2 slot, with my HD in the sata 1 slot, and the m.2 SSD in the m.2 (1)slot.

It does post however when I put my gpu in the pcie 4 slot, with HD in sata 2 and not even putting the m.2 in at all.

Any thoughts or ideas on what's happening and the ideal setup with these parts? There is another m.2 slot (2) I could try. I am still learning how all these parts are interacting with each other so any suggestions would be greatly appreciated.