In goes the motherboard
With the case prepped and drives installed, it's time for our populated motherboard to join the mix.

Standard enclosures are usually a little tight, so it's easier if you insert the motherboard at an angle, port-side first. Line up the port cluster with corresponding holes in the I/O shield and gently set the board down on the mounting posts you screwed into the case earlier. If the motherboard is positioned correctly, its mounting holes should line up exactly with the posts below.

From here, you'll want to screw the motherboard into place using screws provided with the case. When tightened, the screws should be snug, but there's no reason to really torque on them.

Next, we tackle the case's front-panel connectors for the power and reset switches, power and hard drive activity lights, and the PC speaker. Each motherboard lays these connectors out in a slightly different fashion, so you'll have to consult the manual to determine which connectors plug in where. For hard drive and power LEDs, colored wires should be plugged into the positive pins on the motherboard.

It's ridiculous that the industry hasn't agreed to a standard for front-panel connectors that would eliminate the need to connect a mess of wires individually, but this is the system we're stuck with. Be sure to plug in the front-panel connectors now, because things only get more crowded inside the enclosure from here.

While we're connecting front-panel hardware, it's worth tackling expansion ports. Most enclosures now come with front-mounted USB ports that hook into headers located on the motherboard. Depending on your case, these front-mounted USB ports may be tied to a series of wires that have to be connected individually, or they may connect with consolidated blocks that can be plugged in all at once. Obviously, the latter is much easier to deal with. If your case's front-panel USB ports are attached to individual wires, you'll need to consult your motherboard manual for a diagram illustrating how those wires should be connected to pins on the motherboard.

We've only addressed USB headers here, but the same applies for front panel Firewire, eSATA, and even audio ports. The wires for each front-panel connector should be clearly labeled, either on the wires themselves or in the manual that comes with your case. Your motherboard's manual should have full pin diagrams for all its onboard headers that illustrate how these leads should be connected, as well.

Expansion cards join the party
There are only a few pieces we need to put into place to complete our build, and next up, we have expansion cards. Most systems will require at least one expansion card—graphics, of course—but some folks may also have a discrete audio card, TV tuner, or other auxiliary hardware to complement their motherboards' integrated peripherals.

Before installing expansion cards, we need to make some room for them in the case's back plate panel. Our screwdriver comes out again, this time to remove back plates corresponding to the slots in which we intend to install our expansion cards. Keep in mind that for most double-wide graphics cards, you'll need to remove two PCI back plates—one across from the expansion slot and a second back plate immediately to the left.

To seat an expansion card, place it into an appropriate expansion slot and apply even pressure along the top edge of the card until it slides into place. When properly installed, the card's back plate should line up flush with the enclosure. Now use the same screws that held the case's empty back plates in place to secure the expansion card to the case.

The expansion card installation process is the same whether you're putting in a graphics card, audio card, or any sort of other peripheral. Just make sure that you're using the correct type of slot, be it PCI, PCI Express, or with older systems, AGP. Like most PC components, cards are keyed only to fit into a slot one way, so you shouldn't have a problem.

You'll note that in the picture above, we're installing the system's sound card in the lowest expansion slot. At the very least, you should avoid putting expansion cards right next to your graphics card—doing so can impede airflow to the graphics cooler. I tend to put other expansion cards into the lowest slots to give the graphics cooler as much room to breathe as possible.