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I have a desktop PC which was recently moved. Since moving I've noticed that even while the PC is turned off (but wall socket turned on) the NumLock LED on the keyboard is on.

It may have been doing this before the move, but I've only noticed it now.

Maybe it matters that the keyboard is connected via a shared mouse/keyboard PS/2 port and I'm running Windows 7.

I've not checked whether the LEDs are just keeping whatever state they were in when I turned the PC off but will do this if that information could be relevant.

Why does the led stay on when the PC is turned off and how can I prevent this?

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  • Have you removed all the other cables connected to the PC? Sometimes the power comes in from an external device such as a self-powered USB-Hub.
    – Robert
    Sep 17, 2012 at 11:04
  • Nothing connected to the PC has its own power supply apart from the monitor. The socket on the wall and on the PSU are both on though. Sep 17, 2012 at 11:07

6 Answers 6

17

The behavior is of the keyboard LEDs being ON is fine, and it stays on because:

  • After a normal / successful shutdown, the motherboard LED is on, and that means the motherboard is still receiving power.

  • As long as the motherboard receives power, it will give +5V AUX supply. The +5V AUX voltage is what is used to power up the system.

  • It can also power the USB ports when the PC is off if your motherboard supports that function.

  • It also maintains the state of the LEDs on the keyboard as far as my knowledge goes, for example if your NumLock was ON when your PC was ON, then it will remain ON

The only way you can prevent it is to shut off the power from where it is plugged in, or just pull out the power cord connecting your SMPS / PSU from the back of your CPU.

For more reference and details read this on SevenForums. He does mention that even his NumLock remains ON along with his motherboard LED.

4

It could be that the computer is waiting for a 'wake on HID (Human Interface Device, e.g. keyboard)'. This is especially likely if you are hibernating instead of actually turning it off. There may also be a BIOS setting controlling this.

You could try hitting a key and seeing if the computer wakes. It may not necessarily do this, and if you don't need wake on keyboard you may as well disable it anyway.


You could try disabling wake on keyboard in the Windows 7 device settings:

  1. Open the Device Manager

  2. Find your keyboard, right click, Properties

  3. Go to the Power Management tab

  4. Uncheck Allow this device to wake the computer


You could also take a look at your BIOS settings for something related. I can't give more precise instructions on that.

1

Certain desktop and laptop motherboard manufacturers came up with an idea to supply power to USB devices even if the computer is shutdown. As long as the power supply is plugged in and receiving electricity, devices attached to the computer will receive power.

This is a motherboard feature, and not dependent on the operating system.

To control when this is enabled (if at all), check the documentation for your motherboard or your desktop manufacturer. It will be a BIOS setting that you can change.

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  • I have noticed this behavior with external keyboards plugged into a laptop but never in a desktop system, so I agree with this answer. You can simply unplug and re-plug the keyboard to turn it off.
    – Synetech
    Sep 17, 2012 at 15:32
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Here is the solution for Windows 7: Run regedit, navigate to HKEY_USERS\.DEFAULT\Control Panel\Keyboard and change InitialKeyboardIndicators text value to 0. If you are on Ubuntu, my only solution is flipping the hardware jumper located close to the PS/2 port on the motherboard. Older motherboards had this also available for USB ports, not so much today.

P.S.: I knew it had to be in the OS when XP always could do it. The person talking about it being impossible is not an IT problem solver.

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I may have the solution for this sometimes the keyboard is knocked and say like you added a mouse to the back of the system and knocked the keyboard slightly all I did is just this pull the keyboard out and replug it in again making sure the power is off or in shut down

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So I'm having sort of the same issue BUT my numlock LED stays on after my PC shuts down sometimes and in addition to this when I wake up to go to work its still on but when I go to look at it directly it turns off! Almost like its watching me and waiting for me to look before it turns off.

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