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Question

my pc not turning on but motherboard led is?

By adamdff ·
Tags: Hardware
hello, i was wondering if you could help me dove this situation. i’ve just finished building my pc and plugged all the cables in. but there’s a problem. only the LED on the motherboard will turn on, nothing else. i cant see to what seems to make this happen, it can’t be the psu because how would the led turn on? (the led was turned on by the 24 pin)
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Maybe in the future that LED could mean that.

by rproffitt Moderator In reply to my pc not turning on but ...

You left out all the detail but soon we'll be using a new design PSU and motherboard that only takes in a single +12 Volt supply. But today most PSUs have 3.3, 5, 12 and maybe a few more rails so the LED tells us very little.

The usual problems we see are and in no particular order are:
1. The other PSU cable called ATX12V or "CPU Power" is not plugged in.
2. The CMOS RESET JUMPER (can be called by a few names) is on the wrong pins or installed when it shouldn't etc.
3. Some boards shipped with an insulating item on the CMOS battery and the builder forgot to remove it (read the fine manual?)
4. The machine has a build issue such as too many motherboard standoffs or other short that the builder created.
5. The CPU is not on the support list.
6. If there is a graphics card, the builder sometimes forgets to power this board. Varies with model.

There are hundreds of YouTube videos about each of these issues but as you can tell, the LED doesn't tell you much here.

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Yes it can be the Power Supply

by The Master2 In reply to my pc not turning on but ...

The LED Glowing only tells you that there is power well voltage on that rail most likely a 3.3 V Rail but it doesn't tell you there is any current or voltage available on any other Voltage Rail.

The 3.3 V is the Logic Rail and provides power to the CPU and very little else.

The number of times someone has brought in a dead computer where they have replaced everything but the Power Supply because that LED Glows so it cannot be the Power Supply is amassing and they fact that they refuse to believe that the PS has died even when you shove a Power Supply Tester onto the leads and show them that there is no voltage on the 12 V Rail they continue pointing to the LED and insisting that the PS works and it doesn't matter you plug in another one in front of them and power it up and the thing runs. It can not be the Power Supply because that LED glows and it means absolutely nothing at all.

Anyway start at the beginning test everything start by removing everything from the case place the M'Board CPU and Ram onto some clean white paper and then plug in the Power Supply and some test leads to the front panel switches and Led's then plug in the Power Supply and turn it on if it has a Power Switch on it then push the On Switch and see what happens.

If nothing happens reduce the thing to a CPU 1 RAM Module and try again but first make sure to unplug the PS or you'll run the risk of killing the M Board when you remove things with Power on. ATX Power Supplies provide 5 V DC all the time power is available to the Power Supply for little things like the Real Time Clock on the M'Board so the BIOS Settings do not disappear and stop the unit booting.

Depending on the M'Board you are using after it boots up you can turn it off and add a video Card and Keyboard if it uses a PS2 Keyboard and very few new ones do these days Do Not Use a USB Keyboard as the drivers for it are not loaded till the OS is loaded so you can not set the BIOS.

After it works out of the case you can turn off the Power Supply unplug it and dismantle the entire thing down to the M'Board and fit that tot he case and then add the Front Panel Switches and Light Connections and a Video Card if it needs one. With New Video Cards most have a Aux Power Plug on them and this needs to be plugged in for the thing to work. Also the M'Boards have a secondary Power Plug tot he Main one which is a 24 Pin Plug this secondary plug can be 4 6 or 8 Pins and needs to be plugged in for the thing to work.

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