Baring some DOA part, check and recheck everything, case and PSU connectors etc. Take out of the case and assemble just main parts outside. Reset CMOS if you didn't do it already. It shouldn't happen but check http://www.asrock.com/MB/AMD/X370%20Killer%20SLIac/index.asp#CPU
looks like it needs BIOS v P2.0 to work with "X" processors.