I was having an issue when I built my PC - it would go into a boot loop and after 4/5 attempts it would boot.
My issue turned out to be a faulty power supply (which I had been using for a couple years) once that was replaced no issues.
I was told by tech that there is a memory timing issue with Sandy Bridge though. Go into your bios and change the memory settings to XMP if you are using memory with a speed over 1600 mhz. If you aren't set to XMP and the native speed is over 1600mhz the PC can cold boot as it lowers the memory speeds in order to boot.