A few things I check when I have problems are the little spring like things on the back plate (sometimes they get inside the motherboards plugs when sliding the mobo back) and rechecking the screws and mount positions I used. Not every hole on a motherboard is meant to get a standoff and screw. When the engineers design them they do so with 10 different types of boards around the same basic design and some boards will use one screw hole and not another. The way to check is to look for solder around the hole that lets you know its meant to ground to the case. If there is no solder around the mount hole do not put a standoff or screw there.
Both of those common errors involve a direct short, except for losing a screw during building and it gets behind the board, those are the most common ways to create a short on your own. The other common error people make is when mounting the case power and led wires to the board. The rule is, if its a switch (power button reset button) then it doesn't matter which one goes where. But is its a device (led speaker) it must follow polarity, positive to the tiny + sign and negative to the - sign or (red plus/black minus). In the event you end up with a red and a white the white will be minus, red is always plus.
And one other thing is to make sure you used the right connector for the CPU fan, I have seen two connectors close to one another, one for the powersupply fan and the other for the cpu. If you use the wrong one the board will think there is no fan and shutdown as soon as the cpu attempts to power up.
