Here are the motherboard power connectors, with the SATA power cables in the red rectangle on the bottom. The motherboard connectors are plugged in, but the SATA connectors aren't yet. Be careful how you connect these motherboard connectors and make sure the clips line up and snap into place for both the left and right connectors shown. If you reverse it, or worse, shift it over (which is pretty hard to do), it's possible you'll see smoke coming out of the motherboard when you try to plug it in and turn it on. I've seen someone do this before, and it isn't pretty. If nothing snaps into place and you can easily pull it out without having to squeeze on the release clips, it's plugged in wrong.
CNET Networks / TechRepublic