How to Turn On a Computer

Before pressing the power button, you should check a few things first. This guide walks you through each step to make sure your desktop computer starts up correctly. You'll also learn how to fix common problems when your computer won't turn on.

What You Need Before Starting

Before turning on your computer, check that these basic parts are connected. If any of these are missing or loose, your computer might not start or show anything on the screen.

• Power cable plugged into the computer and a wall outlet
• Monitor connected with a video cable (HDMI, DisplayPort, DVI, or VGA)
• Keyboard and mouse plugged into USB ports
• Power supply switch on the back set to ON
• Monitor turned on with its own power button

Step 1: Check the Power Connection

Find the power cable at the back of your computer. This thick cord connects your computer's power supply unit (PSU) to the wall outlet. Look for a small switch near where the power cable plugs in. Make sure this switch is set to "1" or "ON" instead of "0" or "OFF".

Also check that the other end of the cable is plugged into a working outlet. You can test the outlet by plugging in a lamp or phone charger to see if it works.

Step 2: Connect Keyboard and Mouse

Your keyboard and mouse plug into ports on your computer. Most computers today use USB ports. Some older computers have round PS/2 ports instead.

USB Connections

USB connectors are rectangle shaped. You can plug them into any USB port on your computer. These ports are usually on both the front and back of the case. Almost all keyboards and mice made today use USB.

PS/2 Connections (Older Computers)

Older computers use PS/2 ports with round connectors. The purple port is for keyboards and the green port is for mice. You must plug these in while the computer is off, or you could damage the motherboard.

Step 3: Connect Your Monitor

Your monitor needs two connections: a video cable to show the picture and a power cable to turn on. There are several types of video cables you might use.

VGA Connection

VGA is an older type of video cable with a blue connector and 15 pins. It has screws on each side to hold it in place. VGA only works with lower screen resolutions and is mostly found on older computers.

DVI Connection

DVI gives better picture quality than VGA. It has a white connector with many pins and usually has screws to hold it tight. DVI was popular before HDMI became common.

HDMI Connection

HDMI is the most common video cable today. It carries both picture and sound through one cable. You'll find HDMI ports on most computers, monitors, and TVs.

DisplayPort Connection

DisplayPort gives the best picture quality. It works with high refresh rates (144Hz, 240Hz) and high resolutions (4K, 8K). Gaming monitors often use DisplayPort for the smoothest picture.

Step 4: Turn On Your Monitor

Your monitor needs its own power to work. Some monitors use a power adapter (a small box on the cable), while others plug straight into the wall with a regular power cord.

If your monitor has a power adapter, make sure both ends are plugged in firmly: one end goes into the monitor and the other into the wall outlet.

Monitors with regular power cables work just like your computer. Plug one end into the back of the monitor and the other end into a wall outlet.

Step 5: Press the Power Button

Now that everything is connected, find the power button on your computer. It's usually on the front of the case. You might see small lights or other buttons nearby.

Press the power button once and let go. You should hear fans start spinning and see lights turn on. Most computers with modern solid state drives (SSDs) take about 30 to 60 seconds to fully start up.

What to Do If Your Computer Won't Start

If nothing happens when you press the power button, try these steps to find the problem.

• Check that the power supply switch on the back is set to ON (not OFF or "0")
• Make sure the power cable is plugged in firmly at both ends
• Test your wall outlet with a lamp to make sure it works
• If you're not sure which button is the power button, try pressing different ones
• Wait about 15 seconds between button presses so you don't miss any response

Nothing Happens at All

If you don't see any lights, hear any sounds, or see fans spinning, the problem is probably with the power. Check all your power cables again and make sure the power supply switch is turned on.

Computer Turns On But Screen Stays Black

If you hear fans running but don't see anything on screen, check your monitor. Make sure the monitor is plugged in, turned on with its own power button, and connected to your computer with a video cable.

What Happens When Your Computer Starts

When you turn on your computer, it goes through several steps before you see your desktop. Knowing these steps can help you figure out where problems happen.

1. Power-On Self Test (POST): Your computer checks its own parts like RAM memory, storage drives, and graphics card to make sure they work.
2. BIOS/UEFI Screen: You might see a quick screen with your computer maker's logo. This is the BIOS or UEFI getting your hardware ready. Learn more in our guide on how BIOS works.
3. Operating System Loads: Your operating system (like Windows, macOS, or Linux) starts loading.
4. Login Screen: You see either a login screen or your desktop, and your computer is ready to use.

If your computer with a connected monitor stops at any of these steps, that tells you where the problem might be.