System not starting - nothing at all

[Fat Tony]

I built a PC and it ran flawlessly for 5-6 months.
I went to power it up a few days ago ... and absolutely nothing on any part of the system appears to be working. No lights on motherboard/case/fan, etc.
I initially assumed it was the PSU and got that replaced but still, nothing happens at all.
How do I diagnose the fault and fix it? Must it therefore be the motherboard?

It's a simple system, with no GPU (yet):
MB: Z270I GAMING PRO CARBON AC LGA1151 Intel Z270 DDR4 ATX
CPU: Intel Core i5-7500 3.4GHz 6MB
PSU: EVGA SuperNOVA 550 G3, 80 Plus Gold 550W
Cooler: Master Hyper 212 LED CPU Air Cooler

 

[alexoiu]

Try clearing the CMOS (unplug the power cord and remove the CMOS battery for a minute). If still the same, it might be a defective board and you could try RMA-ing it.

 

[Fat Tony]

Alexoiu - it worked. You sir, are a genius! Thank you.
I just looked up CMOS in the manual and pressed the button at the back of the input plate.
What a lot of trouble and time I wasted.

 

[alexoiu]

You're welcome.