|"I have a new "Power up" LT 400w atx psu"|
It's a cheapie & not a goodie. Not enough amps on the +12v rail for a modern system. You should have no problem benchtesting with it, provided there's nothing wrong with it:
Are you sure the CPU & heatsink are installed correctly? Make sure you don't have a mouse connected to the board & use a PS/2 keyboard, not USB. Why are you using the HDMI port for testing? If your monitor has VGA or DVI, try one of those instead. When you attempt to boot, do the cooling fans come on & stay on, or do they stop? Also, did you try booting without any RAM installed? The board should beep like crazy.