If you've just built a new computer from the ground-up; and the darn thing won't POST, here's a few useful links that will be able to narrow down what the problem is
Help, my PC with Windows 10 won't shut down properly
Since upgrading to Windows 10 my computer won't shut down properly. I use the menu button shutdown and the screen goes blank, but the system does not fully shut down. The only way to get it to shut down is to hold the physical power button down till it shuts down. Any suggestions?