Connect the 24-pin motherboard connector before anything else

The 24-pin ATX power connector is the main power line to your motherboard and should be your first connection. This cable carries power to the CPU, RAM, and all the slots and headers on the board. Without it seated firmly, nothing else will work — not the CPU power, not the fans, not the case lights.

Push the connector straight in until you hear or feel a click. The plastic tab on the side of the connector should align with the notch on the motherboard header. If it does not slide in smoothly, stop and check the alignment rather than forcing it. A misaligned connector can bend pins inside the header and damage the board permanently.

Key Takeaways

  • The 24-pin ATX motherboard connector must go in first because the motherboard cannot receive any power without it.
  • The 8-pin CPU power connector (or 4-pin on older boards) goes in second, usually near the top of the motherboard above the CPU socket.
  • SATA power and PCIe power connectors for graphics cards come after the main power lines are seated.
  • Check that each connector clicks into place and sits flush against the header — a loose connection can cause the system to fail to start or shut down unexpectedly.
  • Leave the power supply switched off until all connections are complete and you have double-checked them.

The 8-pin CPU power connector comes second

After the 24-pin motherboard connector is seated, connect the 8-pin CPU power cable (sometimes labeled EPS or CPU_PWR on the motherboard). This cable sits near the top of the board, usually above or to the left of the CPU socket. Some older boards use a 4-pin connector instead, and some high-end boards have both an 8-pin and a 4-pin for extra power delivery to the processor.

This connector also has a plastic tab and notch system. Align them before pushing in. The 8-pin connector requires more force than the 24-pin, but it should not require you to bend the cable or strain the motherboard. If you meet real resistance, check the orientation again.

SATA power and PCIe connectors come after the main lines

Once the motherboard and CPU are powered, connect power to any other components that need it. If you have a graphics card, it may need a 6-pin or 8-pin PCIe power connector (or both). These cables usually run from the power supply to the card itself, not to the motherboard. Check your graphics card manual to see which connectors it requires.

SATA power connectors go to storage drives — solid-state drives (SSDs) on M.2 slots do not need power, but 2.5-inch SSDs and 3.5-inch hard drives do. SATA connectors are L-shaped and keyed so they only fit one way. They are harder to damage than the larger connectors, but they can still come loose if not pushed all the way in.

Why the order matters

The order protects your motherboard from power surges and ensures that the most critical components get stable power first. The 24-pin connector is the backbone — if it is loose, the board will not POST (power on self-test), and you will not know whether any other connections are working. The CPU power comes next because the processor needs when ready, stable power to run the boot sequence.

Connecting everything at once and then powering on can mask which cable is loose or misaligned. If the system does not start, you will have to check all of them. Connecting in order lets you verify each step as you go.

How to check that connectors are seated properly

After you push in each connector, look at it from the side. The connector should sit flush against the motherboard header — no gap between the plastic housing and the board. Gently tug on the cable to make sure it does not slide out. If it does, remove it and reseat it.

The 24-pin and 8-pin connectors have a small plastic tab on one side that catches on a notch in the motherboard header. You should hear a soft click when the tab locks into place. If you do not hear it, the connector may not be fully seated. Do not rely on the click alone — always check visually that the connector is flush.

For SATA connectors, the L-shaped notch should align with the key on the motherboard header. Push straight in until you feel resistance, then push a bit more. SATA connectors can feel loose even when they are properly seated, so the visual check is more important than the feel.

What to do if a connector will not fit

If a connector resists going in, stop when ready. Do not force it. The most common causes are misalignment and trying to insert it backward. Remove the connector completely and look at both the cable end and the motherboard header. The notches and tabs should line up perfectly.

Some cables are labeled on the plastic housing — the label should face outward or upward so you can read it. If the connector still will not fit after you have checked the alignment, look for a second identical header on the motherboard. Some boards have multiple 8-pin headers or multiple SATA headers, and you may have been aiming for the wrong one.

If you are certain the alignment is correct and the header is the right one, take a photo and compare it to the motherboard manual. A bent pin inside the header or a manufacturing defect is rare but possible. Contact the motherboard manufacturer before you proceed if you suspect damage.

Power supply switch position during assembly

Keep the power supply switched to the OFF position (or unplugged) while you are connecting cables. This prevents accidental shorts if a cable touches a metal part of the case or another component. Once all the main connectors are in place and you have double-checked them, you can switch the power supply on and attempt to start the system.

Even after the power supply is on, the system will not start until you press the power button on the case. That button is wired to the motherboard through a small header connector that you will have connected earlier during the build process.

Frequently Asked Questions

Do I have to connect the 24-pin before the 8-pin?

Technically no — the system will not work without both, and the order does not affect the hardware. Connecting the 24-pin first is a best practice because it lets you verify the main power line before you move on. If the system fails to start later, you will know the motherboard power is good.

What if my power supply has two 8-pin CPU connectors?

Some high-end boards and power supplies have two 8-pin CPU connectors for extra power delivery to the processor. Check your motherboard manual to see if your board has two CPU power headers. If it does, connect both. If your motherboard has only one, you only need to connect one cable.

Can I connect the graphics card power before the motherboard power?

You can, but it is not recommended. The motherboard needs power first so the system can recognize the graphics card and allocate power to it. Connecting the card power without motherboard power will not damage anything, but the card will not work until the motherboard is powered.

What happens if a connector is loose?

A loose connector will usually cause the system to fail to start or to shut down unexpectedly during use. The motherboard may not POST at all, or it may start and then power off after a few seconds. Reseating the loose connector almost always fixes the problem.

Is it okay to leave the power supply on while I connect cables?

No. Always switch the power supply off or unplug it before connecting or disconnecting any cables. A live power supply can cause a short circuit if a cable touches metal or another component, which can damage the motherboard, power supply, or both.