What could be the reason if the computer does not turn on?

Question

Do it yourself

Hello! Faced such a problem for the first time in practice, there is a computer on the 1150 socket, after work it suddenly turned off and does not turn on.
The first step was to change the power supply to a known working one, to no avail. Following this, a new motherboard was purchased, and then there was a shock, the computer also did not turn on.
Has anyone encountered this? (Check the button, close the power supply, pull out the components, and so on, do not suggest :) )

Answer 1

Launch a new motherboard with a new power supply on the table)))

Answer 2

Test the RAM on a known working motherboard.