PC doesn't start. Power lights blink once

Question

When I press the power button of my PC, it sometimes powers on.

Most of the time, it gives a short flash and nothing else.

Then I have to either press and hold the power button for about 20 seconds and try again or switch of the power supply and then try again after some time.

These is what I tried and doesn't work:

1. Tried different Power cords.
2. Tried different Wall sockets.
3. Tried replacing CMOS cell.

These didn't work.

I tried unplugging the 4 pin connector from the PSU to motherboard and now it starts instantly every time.

But I see nothing on screen. Maybe the CPU isn't running now.

I tried powering it up having the case in an angle. Sometimes at some angles it works.

So I can't figure out what exactly the problem is. I doubt the CPU and the PSU.

Can you suggest what could be the possible cause?

Solution

Possible Solutions:

1. Check if the power switch wires are properly connected to the motherboard in the correct pins. They should be labeled.

2. Remove the CPU and try starting up the computer. Most motherboards will give you an error. If you successfully see this error then you can assume that the CPU is causing problems.

3. Some motherboards have a built in power and reset switch. If yours does, try using those instead.

4. When you disconnect the 4 pins from the motherboard, if you have a dedicated graphics card then try to connect the video cable to your onboard graphics in an attempt to get something to display rather than the graphics card.

Comments

[Alex]

The power button is connected to the motherboard with a few colored wires. Check those wires and the pins on the motherboard.

[DavidPostill]

Could be a damaged power button.

[S Praveen Kumar]

But when I unplug the 4 pin connector and press it works. So I think Power button mayn't be the issue.

[S Praveen Kumar]

The power pins are connected properly. I removed the CPU and powered on. It powers on everytime without any issues. No signs of errors but it powers on everytime as it was when I unplugged the 4 pin connector.

[TheAmazing31]

I would assume it is a faulty CPU, check the CPU socket on the motherboard and make sure none of the pins are bent or damaged. Secondly check to see if the CPU has any damaged connectors. If all else fails the only thing I would assume to be wrong is that you are using a CPU that does not match the socket on your motherboard.

[S Praveen Kumar]

Thank you for your reply. I am sure that the CPU is a compatible one as I am using the same for more than 3 years before getting this problem. I checked the socket for damaged pins, no such pins were found. Could it be the power supply that comes to the CPU via the 4 pin connector?

[TheAmazing31]

That is defiantly a possibility. You could test to see if the power supply is the issue using multiple methods. 1: if you own a multimeter, wire it up to a positive and negative pin from the power supply. Be careful and maky sure you have the write pins by looking up the pin outs of a CPU power connector. 2: if you have another power supply lying around, you are able to short 2 pins (with a paperclip or something like that) that are in the motherboard connector, again make sure you connect the correct pins. If I remember correctly it is a green and a black wire.

[S Praveen Kumar]

I don't have another PSU lying around. I already tried the paperclip trick long back. The PSU runs well(the fans run). Lemme try with the multimeter

[TheAmazing31]

I meant to say to use the paperclip trick on a spare PSU with only the CPU connector connected, but that doesn't matter since you don't have a spare. How did the multimeter go?

[S Praveen Kumar]

I'll try and say the results when I get time.