Don't put a box back together until you're sure it's working.
Never bolt the sides back onto a computer you're building until you're absolutely, positively, cutting-charge-wrapped-around-a-major-artery serious that it's working exactly the way it's supposed to. Installing a server in the rack before the systemware's installed and patched and the servers are up and running is a sure-fire way to provoke a hardware failure or hard drive crash.