Cleaning time
By now, the inside of your case probably looks like a tangled mess of wires, some of which are likely still hanging over the edge. The mess not only looks bad, but it can also impede airflow around important system components. We should really tidy the mess up with a little help from a fistful of zip ties.

First, gather any unused power supply leads into a neat bundle and zip tie them together. This bundle can be stuffed out of the way into your case's empty 5.25" drive bays. Empty 5.25" drive bays make a good dumping ground for excess cabling because they generally don't have venting or fans that might otherwise be obscured by a clump of wires.

With excess power supply leads out of the way, we can turn our attention to the cables we're actually using. There are a number of ways to deal with these, depending on just how clean you want the inside of your case to look. We won't go overboard here, but it's worth taking the time to remove any slack in the cables and carefully route them along the case's internal structure. Most cases have loops or cutouts that can serve as anchor points for zip ties, making it much easier to snake cables out of the way.

Your case's internals don't have to be immaculate when you're finished, but you shouldn't have cables impeding airflow around any components or case fans, or around case vents. Cleaning up internal cabling also makes it easier to work on the system later on, either to swap out components or add new ones when your brand-new system becomes hopelessly out of date after just a few short months.

We're finished with the hardware now, so you can put the case panels back on, stand the case up, and start connecting peripherals like your monitor, keyboard, and mouse. Now would be a good time to plug in the power cord, as well, and to make sure that the power supply is switched to its on position. Hit the case's power switch, and the system should spring to life.

Leaving the hardware behind
Software setup is far too broad for the scope of this build guide. However, before we leave you at the mercy of your operating system installation, there are a few loose ends we need to tie up in the BIOS. With most motherboards, you can get into the BIOS by hitting the Delete key right after the system powers on.

Each motherboard's BIOS interface is a little different, but most follow the same basic conventions. If you're new to building PCs, you don't want to spend too much time poking around. If you're not careful, changing some settings can actually harm system components.

The first thing we want to do in the BIOS is check to make sure that our processor's power management features are enabled. These features will have to be invoked by the operating system, but if they're not enabled in the BIOS first, they won't work.

In systems with Intel processors, thumb through the BIOS menus looking for SpeedStep and the C1E Enhanced Halt State, both of which should be enabled or set to auto. With AMD CPUs, look to enable an option called Cool'n'Quiet. These CPU-specific power management features will likely be found in BIOS sections pertaining to advanced features or power management. Some BIOSes will keep them in a general tuning section.

Next, check to make sure that the BIOS has set the correct clock speeds for the front-side bus and memory. Clock speed control is usually found in an overclocking section of the BIOS, and you don't want to mess with it unless you know what you're doing.

Overclocking instruction is well beyond the scope of this guide, and we wouldn't recommend running your first custom system build at higher-than-stock speeds, anyway—at least not for a while.

Once you've confirmed your system's clock speeds, find the BIOS's memory timing controls. Your memory modules will be rated for specific latency timings at a given clock speed. The BIOS should detect these defaults automatically, but if it doesn't, you can set them manually. Just be sure that the memory timing settings that you use correspond to the capabilities of your memory modules.

Depending on your DIMMs, you may also need to raise the motherboard's memory voltage. This setting will most likely be found in an overclocking menu, usually as the DRAM voltage. Be sure to set this voltage only as high as is required by your memory modules.

The final element of the BIOS we need to touch on is fan speed control. Options vary considerably from motherboard to motherboard, but you want to make sure that automatic fan speed control, often referred to as "smart fan," is enabled if it's an option. You may also see a fan option asking whether you're using a three- or four-pin fan, sometimes referred to as DC and PWM, respectively. Select the appropriate fan type based on your processor cooler type.

If you're lucky enough to have a BIOS that provides extensive fan speed control, take this time to explore the fan speed options. The defaults are usually adequate, but you may want to revisit them later if you find your system running too hot or too loud for your tastes.