Quick answer
First check that the power supply is plugged in and the switch on the power supply is in the I position. Then unplug the computer, open the case, and check that the power cable is properly connected to the motherboard. If it still does not respond, test the power button and the power supply.
How to recognize the problem
- The computer does not respond when you press the power button
- Fans do not start, no lights on the case
- The computer turns on for a moment and then immediately turns off
- The power button feels loose or stuck
Most common causes
Power supply is not turned on or the cable is loose
The power cable may be unplugged from the outlet or from the power supply, and the switch on the power supply may be in the 0 position. Check all connections before assuming a fault.
Faulty power button
The button on the case may be mechanically damaged or stuck, so it does not send a signal to the motherboard. Sometimes it is enough to clean or replace the button.
Power supply failure
The power supply may stop supplying power due to wear or component failure. Symptoms include a complete lack of response or brief power-on.
Loose cable inside the case
The main motherboard power cable (24-pin) or the CPU cable (4/8-pin) may be loose. Check that they are properly seated.
Short circuit or faulty motherboard
A metal object or a faulty component can cause a short circuit that prevents power-on. This requires careful inspection.
Step-by-step fix
- 1
Check the power supply and cables
Make sure the power cable is firmly plugged into the computer and the outlet. If the power supply has a switch, set it to the
I(on) position. Also check that the extension cord or outlet works (try another device). - 2
Unplug the computer and open the case
Before any work inside the case, unplug the power cable from the outlet. Wait a few minutes and, if necessary, hold down the power button to discharge residual power. If the computer is under warranty, check the terms before opening the case. Then carefully open the side panel of the case (usually a screw is removed or a mechanism is opened). Before touching components, touch an unpainted metal surface of the case to protect against electrostatic discharge.
- 3
Check power connections on the motherboard
Locate the main 24-pin connector and the CPU connector (4 or 8 pins). Make sure they are firmly seated and not damaged. Gently press each connector to ensure it is fully seated.
- 4
Test the power button
Disconnect the cable that runs from the power button to the motherboard (usually labeled
PWR_SW). Before this test, plug the power supply back into the outlet and turn on the switch on the power supply. Then, only if you have experience, use an insulated screwdriver to carefully briefly short the two pins on the motherboard where that cable was connected. Do not touch other pins and do not leave the tool in the case. If the computer turns on, the button is faulty. - 5
Check the power supply switch and fuse
Some older power supplies have a small voltage selection switch (110/220V). If present, set it to the value that matches the mains (220V/230V). Do not open the power supply or check the internal fuse yourself; if the power supply has an external user-replaceable fuse, check it according to the instructions, otherwise leave the check to a service center.
- 6
Test the power supply with a multimeter (optional)
If you have a multimeter and experience, you can check the power supply output voltages according to the manufacturer's instructions. To start the power supply on its own, you usually need to briefly short the green PS_ON wire to a black ground, but do not do this without proper protection and knowledge. Do not open the power supply case. If there is no voltage, the power supply is probably faulty. This step is for advanced users.
- 7
Replace the power supply or button
If you suspect the power supply, borrow a working power supply of appropriate wattage and connectors and replace it. Before replacement, unplug the power supply from the outlet. If the button is faulty, you can replace it or temporarily use the power button on the motherboard (if present).
- 8
Check for a short circuit
Remove all components except the motherboard, processor, one memory module, and power supply; if the processor does not have integrated graphics, also leave the graphics card. If the computer then turns on, gradually reinstall components one by one to find the cause. Before each reinstallation, unplug the power supply from the outlet. Pay attention to loose screws or metal parts that may touch the board.
If nothing helps
If you have checked the power supply, cables, and button, and the computer still does not respond, the motherboard may be faulty or there may be a deeper fault. In that case, further disassembly without experience is not recommended. Contact a service center or IT support. Also, if the computer is under warranty, do not open the case yourself as this may void the warranty. For older computers, consider whether repair is worthwhile compared to buying a new power supply.
How to prevent it
- Regularly check that power cables are firmly connected
- Use a quality surge-protected extension cord
- Clean dust from the case to prevent component overheating
- Do not turn on the computer if you notice a burning smell or smoke
When to call a professional
If you are not sure how to safely open the case or test the power supply, it is better to call IT support. Also, if the computer is under warranty, do not risk doing repairs yourself.
IT infrastructure maintenance · Servers, networks, backup, security and helpdeskFAQ
How do I know if the power supply is faulty?
If the computer shows no signs of life (fans do not start, no lights), and the cable is properly connected and the switch is on, the power supply is probably faulty. If you have experience, you can test it with a multimeter; otherwise, leave it to a service center for checking or replace it with a working one.
Can I use the computer without the power button?
Yes, but only temporarily and with caution: if the motherboard has power pins, you can use a suitable switch or a jumper. Do not leave the jumper permanently and replace the button as soon as possible.
What if the computer won't turn on after a power outage?
Check whether the power supply survived the power outage. Sometimes it is necessary to unplug the computer from the outlet for a few minutes to reset the power supply. If it still does not work, the power supply may be damaged.