MacBook Air Early 2014 responds to SMC reset but doesn't turn on MacBook responds to Shift+Control+Option+Power button, the magsafe's light color changes from orange color to green momentarily then goes back to orange. So it means the MacBook is still alive.

What could be the possible cause why the machine won't turn on?

UPDATE

It's working again now, after letting it rest for about two weeks since it crashed.

While in the middle of booting (progress bar is not finished) the computer just turns itself off. Tried to turn it on again it just kept on turning itself off while booting.

This permanently fix the boot crashing: https://discussions.apple.com/servlet/JiveServlet/showImage/2-29433214-653435/image.jpg
You probably have defective hardware. The SMC appears to work, so it's simply not allowing power-on due to a problem elsewhere in the computer.