Hang on, it's not meant to be booting with the pins connected. Unplug the 8 pin and gfx card power before doing this, you want no power running through the board in case it leaks. All you're hoping for is the pump to run, and any fans you've still got connected to the psu will spin up
I just run the pump for a while to be honest, can take a few weeks (stupid loop layout here) but eventually it stops making a noise