|OK, you say you're benchtesting, so obviously you have your motherboard outside of the case, sitting on a non-conductive surface such as the motherboard box?|
You should have the CPU & heatsink installed, one stick of RAM & the video card. The power supply's 24-pin plug & 4-pin plug should be connected, the monitor connected to the video card & a keyboard plugged into the PS/2 port (not USB). And if your board doesn't have a built-in speaker, an old case speaker should be connected to allow you to hear any beep codes. Nothing else is required.
Switch on the monitor, switch on the power supply, then use the tip of a screwdriver to short the 2 pins that the case's power switch would normally connect to. The fans should then spin up & the ASUS splash screen should come up on the monitor. If it doesn't, double check all your connections.
BTW, you didn't list your power supply or it's specs. What brand is it? How many watts & what are the amperage specs?