check your power settings in windows and what the start button does.I changed to high power setting and little did i know but windows has further default settings when you choose this and so i had great difficulty booting.The computer would start and the fan come on but nothing else just a black screen.I tried a new switch with restart button and this worked after using start button.The problem was solved by going into windows power settings and unticking any boxes below that setting on what the power button does.This solved years of this problem for me.It was not the memory or power supply at fault.