System not booting with red light near cpu

PCNoobMK3

Prominent
Jul 5, 2017
20
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510
So in late 2016 I build a pc for my nephew but a few days ago he texted me with this info:
My pc wont boot anymore. the fans go on for a lil bit but then it all shuts off with a light flashing near my cpu. No cables are loose and he tried switching the RAM sticks to different slots he tried removing the power cord and leaving it without power for a lil bit. The light flashes 1 time and its a short flash.
What could it be and how do I fix it?

Here are his specs(he sucks with computers so I am the go to guy with problems.):
Intel Core i5-6400 Boxed
MSI H110M GAMING
MSI GeForce GTX 1060 6GT OC
WD Blue WD10EZEX, 1TB
Phanteks Eclipse P400S Black Window
Crucial CT8G4DFS8213
Crucial CT4G4DFS8213
Antec VP700P