Keyboard problems when Num Lock is on.

1

Open Command Prompt, then paste in this command and press Enter:

msdt.exe -id KeyboardDiagnostic

Run that Keyboard Troubleshooter to see if that can solve the problem.

2

If that does not resolve this for you

Open Device Manager

Expand the Keyboards section

Right click your keyboard and choose 'Uninstall'

Then restart your PC

3

If the problem is still not resolved, open the Settings App.

Go to Accessibility - Keyboard.

Ensure the Sticky Keys, Filter Keys and Toggle Keys settings are disabled.

Then go to Accessibility - Mouse and ensure the Mouse Keys setting is disabled.

This behavior is consistent with a hardware fault in the keyboard rather than a Windows setting issue.

When Num Lock is on, the numeric keypad and some other keys share the same internal matrix lines. If part of that matrix is shorted or contaminated (for example, by debris or liquid), enabling Num Lock can cause multiple keys (Ctrl, Alt, B, N, 3, etc.) to appear “stuck” or to generate repeated characters like the period you see in the browser and on the keyboard test site. When Num Lock is off, that part of the matrix is not used in the same way, so the problem appears to disappear, but the underlying hardware issue remains.

To isolate and address the problem:

1. Test with an external keyboard
   • Connect a different USB (or wireless) keyboard to the same PC.
   • Turn Num Lock on and off and check whether the issue occurs.
   • If the external keyboard works normally, the built‑in keyboard is almost certainly faulty.
2. Clean the affected keys
   • Power off the device.
   • Use compressed air to blow under and around the affected keys (Ctrl, Alt, B, N, 3, NumPad keys).
   • Wipe the key tops with a slightly damp microfiber cloth (no liquid entering the keyboard).
   • After cleaning, power on and test again with Num Lock on.
3. Check in Safe Mode
   • Boot Windows into Safe Mode and test the keyboard with Num Lock on.
   • If the same keys appear stuck in Safe Mode, the issue is not caused by third‑party software and points further to hardware.
4. If the problem persists
   • For a laptop: the internal keyboard likely needs professional service or replacement.
   • For a desktop: replace the keyboard; this is usually more cost‑effective than repair.

There is no Windows 10 setting in the provided material that would cause only Num Lock to make specific keys behave as stuck; the documented keyboard options (Sticky Keys, Toggle Keys, Filter Keys, etc.) affect how keystrokes are interpreted but do not selectively break keys only when Num Lock is on. The observed pattern aligns with a failing keyboard matrix.

References:

• keypad issue - Microsoft Q&A
• Make your mouse, keyboard, and other input devices easier to use