How to build a computer
Getting the case ready for the motherboard
As you can see, my case clearly isn't ready for a motherboard. There are cables from the power switch, cables from the fans, cables from the USB ports....all summing up to one big mess. So here's what you need to do before you even think about putting your motherboard in.
The IO Shield
See this? It probably came with your motherboard.
See this? It's the same thing, except with one big difference. The IO shield that came with your case will not let your motherboard fit. You need to replace the IO shield. Some IO shields will pop in and out, but the other ones have screws that hold it down. You need to take those screws off, take off the IO shield, put the IO shield that came with your motherboard in, and screw it in. Now you can relax knowing that at least one part of your motherboard will fit.
When I first saw these in the bag of screws that came with my case, I had no idea what they were or what they were for. These are the single most important screws you will use in your build. To help you understand exactly what they are for, let's pretend that you're not going to use them. How are you going to get the motherboard secured to the case? You are probably going to screw the motherboard directly to the case. And if you screw the motherboard to the case, the whole thing will short circuit, killing your motherboard and quite possibly your processor because the whole backside with all the soldering and pins will touch the case metal. And so, remember the spacers, and you won't have to go through the really long process of RMAing your motherboard and processor.
Install the spacers exactly where you plan on screwing the motherboard to the case, so that the spacers effectively elevate the motherboard and prevent it from touching the case. After you install the spacers, your case should look something like this.