You didn't specify what all is in the loop, but since you mentioned placing the Mobo in first, I assume The cpu and or NB is in the loop.

It is prolly recommended that you test your loop outside the case, where you can set it in a safe position where one leak wont ruin it all!

Just let it run for a small amount of time after making sure all tubing and fittings are on nice and tightly.

(Not to mention it's easier to get air bubbles out of things when you can maneuver the components around.)

But... if you un plug everything else, I dont see a problem, if it explodes with liquid all over, just make sure the junk is dry before you give it any power. And that liquid can be hard to clean, because it lubes as it goes!

I mean, you do know that you did a good job, right?

--Lupi