New system stops booting randomly after 2 weeks of working

[FunGui]

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?

 

[brispuss]

Confirm that video card, DIMM's, all cables (including case power switch cable) are installed properly. Try starting system again.

If there is no response at all, the PSU may be faulty. Try another known working PSU (at hand or borrow one) instead.

 

[FunGui]

Most of my old PC is still functional, I shall do that tommorow

 

[FunGui]

It does not start up to BIOS, non of fans spin (sorry cannot edit on phone)