You've installed the motherboard and power supply, inserted the processor, and installed your RAM modules. Now it's time to connect all the wires on the board. Accuracy in this step is vital, because any errors mean that your PC may not work as it should or may not boot at all. Here are the details.
How to connect your cables to the motherboard
Much like hooking up a home theater system, computers have many cables and wires that tend to mess up. It is essential to know where each wire or connector goes, as well as to ensure the correct order. Follow the steps below to make sure each component is working properly.
1. Where to connect the power button switch wires

In order for your PC to turn on when you press the power button, you need to connect the power switch to the motherboard. Among the loose cables in your case you will find a two-pin connector, which is usually marked PWR SW, but check the case manual if you are unsure.
The power switch wires should be connected to the power jumpers on the motherboard. Typically, these pins are located on the lower right and are usually unmarked.
2. How to properly connect the reset switch wires

If your PC case has a reset switch, the socket is similar to the power button, showing RESET SW rather than Power SW. This connector allows you to restart your PC after an annoying crash, as it resets the hardware and forces your computer to restart.
To connect the reset button wires, you need to find the jumpers on the motherboard. The connector is usually near the power switch. Push the plug over the two prongs to secure it in place. It doesn't matter which way this connector goes.
3. Connecting the power and hard drive LEDs

The HDD connector is connected to an LED on the front of the case which lights up when the hard drive is in operation. This light is useful because it indicates whether your PC is working or has crashed.
Since the wires connect to an LED, they require a specific order to work properly. The cable usually includes positive and negative markings on the plastic plug. The motherboard HDD jumper will also have a positive and negative port. Check your manual carefully to make sure you get this connection in the correct order.
Follow the same procedures as above for the LED power wires, which will have a similar connector. This plug also needs to be attached the correct way round, so be sure to line up the positive and negative connectors.
4. How to connect the USB wires on the motherboard

If your case has front-mounted USB ports or a card reader, you'll need to connect them to spare headers on your motherboard. In all likelihood, the cable in the case is marked as USB.
Your motherboard should have spare connectors marked "USB", but the manual will tell you exactly where the pins are if they exist. USB connectors require power, so you must plug the cable in the correct way. Fortunately, the USB ports found on most PC cases have a single socket that only connects to the motherboard one way. If your PC doesn't have a formed socket, you'll need to check the case and motherboard manuals carefully to make sure you're installing the wires correctly.
Assuming you're using a block connector, plug it into spare USB pins on the motherboard. It's best to use the header closest to the cable to avoid draping the cables all over the place.
5. Installing the FireWire connection to the motherboard

Front-mounted FireWire cables plug into the PC the same way as USB cables. Again, find a spare FireWire header on the board (the manual will explain where these are), then connect the FireWire cable. The plastic connector on the wires may be labeled as 1394, since FireWire is also known as i1394.
6. Connecting the audio wires on the motherboard

The front-mounted audio ports also require a connection to the motherboard if you want to plug in headphones or even a microphone. Luckily, most PC cases have a one-piece jack for all front audio connectors, whether they're headphone jacks, audio inputs, or even microphones.
Your motherboard manual will have full details of where the audio cables connect, which is usually near the rear panel. Again, there's only one way to connect the plug, so gently slide it into place. If your case has a speaker header for warning beeps, plug it into the appropriate connector on the motherboard.
7. Where to connect the fan wires to the motherboard

It is common for modern cases to have additional fans pre-installed in specific areas. These cooling devices help increase airflow inside and outside the case, and they keep your PC cool. Although you can usually connect fan wires to power connectors, it's best to connect them to spare fan headers on the motherboard. Most cards automatically control fan speed and keep your PC running as quietly as possible.
If your fans have three- or four-pin connectors, which they almost always do, they connect directly to the motherboard. These fans are usually the type that offers automatic speed control. Older PCs had two-pin plugs and ran at a constant speed. Check the manual for a spare fan connector, then plug in the fan's power connector. Three-pin connectors can plug into four-pin ports and vice versa. Cables usually only plug in one way, so it's easy to get it right.
8. Connecting the CPU fan wires

The CPU fan is the most crucial connection of all, maintaining a safe temperature for the CPU at all times. Like system fans, CPU fan speed is controlled by the motherboard, based on the CPU's current internal temperature, and it keeps your computer as quiet as possible. Older motherboards/PCs may not offer a "quiet mode" option, but the fan wires still require the correct order, that's why they include fitted plugs.
Also, there is a special CPU fan connector on the motherboard, often labeled CPU FAN. Consult your manual for its location. The socket is probably a four-pin connector, but there are also three-pin CPU fans. The connector only goes one way.
9. Connecting HDD/SSD Data Cables
Similar to the cables you had to plug in earlier, the slot in which to insert them will be labeled. The slots will be labeled SATA1, SATA2, etc. There are usually multiple SATA slots per motherboard.

Now plug your HDD/SSD data cable into the SATA slot.

After connecting your HDD/SSD cable, you are ready to install your HDD or SSD.
Once everything is properly connected, make sure the cables are secured and placed in a safe place. You don't want your wires getting caught in fans or touching hot surfaces. Using empty drive bays and zip ties, you can secure internal cables in your newly refurbished PC.
Useful tips for working on your computer
As with any technical device, there are a few things to consider when working inside your PC for any reason, so "let's start here". Did you catch this pun? Here are four essential steps to take whenever you work on your PC.
- Make sure the power is unplugged – Obviously, this may not apply if you haven't connected the power cable yet, but it's worth mentioning just in case.
- Reduce the risk of electricity status – Natural static in your hands can wreak havoc on internal computer parts. Whether you're using an ESD mat or a safe wristband, this is an important step to take to protect your investment.
- Keep your work area free of any liquids or debris – You don't want to spill a bottle of water on your new computer. Clean up the work area before you start and try to keep the dust down while you're at it.
- Clean your hands – When working with cables and other internal components, oils and dirt on your hands can cause problems later. Powder-free nitrile gloves are best, but clean hands will do.
In conclusion, taking precautions when working on your PC and understanding how to properly connect internal wires and cables means your device will be up and running in no time. You'll not only prevent damage, but you'll also ensure that the lights and buttons work properly and the audio connections work as expected.
Tips for connecting cables
If this is your first time working on electronics or even opening a computer case, there are a few basic tips you should know before connecting components with wires.
Keep your cables organized – Ok, so this one isn't necessarily vital to the health of your machine, but a clean and organized case is absolutely glorifying. If you take a few minutes before you install your components and plan out how everything is laid out, it will be much easier to hook everything up (and replace outdated components later). You can use small zip ties or just neatly store everything in its place.
Keep your workspace organized – Like any project, even this one can be incredibly frustrating. Treat yourself and reduce that frustration by having everything you need where you can find it before you get to work. Also, remove all trash, debris, dust, or especially liquids before opening any packaging. This will ensure that your components are safe and working properly once your project is complete.
Wait to plug your power supply into a wall outlet – It may be obvious, but we need to have warning labels for a reason. Don't electrocute yourself because you neglected to unplug your power supply from the wall before working.
Do not wear jewelry or loose clothing – If you wear wristbands and puffy long sleeves when working on your machine, you'll quickly understand why it's not a good idea (say hello to hanging on to random computer parts and thus increasing your level of frustration).
Use protective equipment – Admittedly, there is a ton of debate about the need for ESD tapes and gloves when working on electronics. But, it's best to err on the side of caution if you don't regularly work with motherboards, capacitors, and other small electronics. The argument for wearing gloves is that oils, dirt, and other contaminants can damage your computer's parts (even corrosion afterwards). The argument for ESD precautions is simply that you could shock a component by damaging it with static electricity.