New system stops booting randomly after 2 weeks of working

FunGui

Honorable
Nov 10, 2013
169
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10,710
About two weeks ago, I built/upgraded a PC. It worked fine, up till about five minutes ago. It was turned on, and I went downstairs for about 20 minutes. I went back upstairs and it had turned off. It will not turn on. Please help me :)
It has the following componants:
4690k@4.2 GHz
Asus Z97-A
Radeon 7770
Passive 460 watt 80+ gold silverstone PSU
Crucial m500 SSD
16gb corsair vengeance

It is too late now, but tomorrow I will check everything is plugged in, and will replace RAM to see if it is that.
Could anyone help?