Question : PC WON'T START FIRST TIME

My pc has started having boot problems, It will not always start first time but if i hit the restart button or start button a couple of times it starts and runs fine,i have tried new hard drive/new memory,updated all drivers,checked all connectios,but cannot resolve this issue,i have some workig knowledge of pc's i have built several in the past.cananyone help please

Answer : PC WON'T START FIRST TIME

Thanks you guys,managed to sort it out myself,
Nothing to do with PSU, It turned out that i have a pci sata connector and i removed it and re-installed driver, oddly it did not show in device manager,
Now everything is A OK.
thanks again to everyone