I fixed that by updating the BIOS - - may not work for everyone but it worked for me.
Now I can do a soft (Windows) restart no problem. Previously I had to shut down & restart because soft restart never worked, it would just hang instead of POSTing.
It had that problem from day one after completing the build. Checked all the connections, was about ready to try a new PSU when I thought here goes, I'll try BIOS update first. Glad I did.