When most of the keyboard works and only some keys fail, do not start cleaning or reinstalling at random. The set of keys that fail is a diagnosis in itself. Press every key in the tester above, note which ones stay dark, and match the pattern below.
Patterns and what they mean
| Pattern | Most likely cause | Go to |
|---|---|---|
| F1 to F12 do the wrong thing or nothing | Fn lock | Function row |
| Letters U I O J K L M type numbers | Num Lock overlay | Number keys |
| Number row types symbols, letters are capitals | Stuck Shift or Sticky Keys | Modifiers |
| Numpad moves the cursor | Num Lock off | Number keys |
| One key dead | Debris or a worn switch | Single key |
| A straight row or column dead | Matrix fault or ribbon cable | Row or column |
| Scattered keys dead after a spill | Liquid damage | Liquid |
| Keys work only when held | Filter Keys or Slow Keys | Modifiers |
| Shift, Ctrl or Alt combinations fail | Modifier stuck, remap, app capture | Modifiers |
| Keys type the wrong characters | Layout | Layout |
Function row
If F1 to F12 change volume and brightness instead of doing their normal jobs, or vice versa, the Fn lock is set. Press Fn+Esc on most laptops, or look for a key with a padlock icon. On a Mac, the behavior is under System Settings → Keyboard → Keyboard Shortcuts → Function Keys. Full details in Function keys not working.
Number keys
Two different problems look alike:
- Letters type numbers. The laptop numpad overlay is on. Press Fn+Num Lock (or Fn+F11, Fn+Insert on some models).
- Numpad moves the cursor or does nothing. Num Lock is off. Press Num Lock and check its light. If the numpad still fails, check Mouse Keys under Accessibility, which turns the numpad into a mouse.
Num Lock not working has the complete list of combinations by laptop brand.
Modifiers
Shift, Ctrl, Alt and the Windows or Command key can fail in ways that look like other keys failing:
- Tap each modifier once to clear a stuck state.
- Turn off Sticky Keys and Filter Keys (Windows: Settings → Accessibility → Keyboard; Mac: System Settings → Accessibility → Keyboard).
- Turn off game mode on gaming keyboards.
- Test in Notepad or TextEdit to rule out an app capturing combinations.
See Shift key not working and Alt key not working.
Layout
If keys register but produce the wrong characters, the keyboard is fine and the layout is wrong. Press Win+Space or Control+Space and read Keyboard typing wrong characters.
Single key
One dead key is usually debris. Blow it out, clean under the keycap, and if it needs a hard press to register the switch is worn. One key not working walks through cleaning and remapping.
Row or column
Keyboards are wired as a grid. The controller scans rows and columns, and a break in one line kills every key on it. That is why a whole row of letters, the entire number row, or a diagonal set of unrelated keys can die together.
- Desktop membrane keyboard: a corroded trace on the membrane sheet. Not repairable in practice; replace the keyboard.
- Mechanical keyboard: a cracked trace or a bad diode on the PCB. Repairable with soldering, or replace.
- Laptop: the ribbon cable from the keyboard to the motherboard may be loose, especially after a drop or a repair. On older laptops the keyboard lifts out and the cable can be reseated. On thin laptops it is a full disassembly.
Before concluding hardware, test in the BIOS or UEFI setup screen. If the same keys are dead there, it is hardware. If they work there, the operating system is blocking them; reinstall the keyboard driver from Device Manager.
Liquid
Scattered failures that appear hours or days after a spill are corrosion spreading. Power off, invert, and dry for 48 hours minimum. Sugary drinks leave residue that keeps conducting; a desktop keyboard can be opened and cleaned with isopropyl alcohol, a laptop needs a shop. Keys that come back after drying often fail again later as corrosion continues.
Work around it
While you decide on a repair:
- Remap dead keys to keys you do not use. How to remap keyboard keys covers PowerToys and Karabiner.
- Plug in an external keyboard.
- Use the on-screen keyboard (Win+Ctrl+O) for the odd key.
- Copy symbols and letters from Copy and paste symbols or the accent keyboard.
Reading the matrix
Understanding the grid helps you predict which keys will fail together. A typical full-size keyboard uses around 8 rows and 16 to 20 columns. Rows usually follow the physical rows, but columns run in odd zigzags to save wiring, so a dead column can take out 1, Q, A and Z on one board, or 7, U, J, M and the up arrow on another. If the set of dead keys looks random, write them down and look for a repeating vertical stripe across the keyboard: that is a column.
Ghosting and blocking are matrix effects too. On cheaper keyboards, pressing three keys that form three corners of a rectangle in the matrix makes the fourth appear pressed (ghosting) or stops one of them registering (blocking). If keys only fail while other keys are held, that is the matrix working as designed, not a fault. Gaming keyboards advertise n-key rollover to avoid it.
Laptop-specific checks
- Fn lock and overlay first; they explain most partial failures on laptops.
- The keyboard cable. On laptops where the keyboard lifts out from the top (older ThinkPads, many business models), unclip it and reseat the flat cable at both ends. On thin laptops the keyboard is under the motherboard and this is a full disassembly.
- Manufacturer diagnostics. Dell (F12 at boot → Diagnostics), HP (Esc then F2 → Component Tests → Keyboard) and Lenovo (Vantage → Hardware Scan) include a keyboard test that runs outside Windows and lights each key as you press it, the same idea as the tester on this page but at firmware level.
Troubleshooting flow
- Map the dead keys with the tester above.
- Function row: Fn+Esc. Numbers: Fn+Num Lock or Num Lock.
- Modifiers: tap each, disable Sticky and Filter Keys, disable game mode.
- Wrong characters: fix the layout.
- One key: clean.
- Row or column: BIOS test, reseat cable, replace.
- Liquid: dry, clean, expect to replace.
- Remap or use an external keyboard meanwhile.
Related
Frequently asked questions
Why does a whole row of keys stop working? +
Keys are wired in a matrix of rows and columns. A dead row or column means a broken trace or a partly unseated ribbon cable, which is hardware. A single key is more often debris.
Why do the number keys not work but everything else does? +
On a laptop, check the Num Lock overlay. On a desktop, the number row is a separate matrix line; if the numpad works but the row does not, it is a hardware fault in that line.
Why do keys work when I press two at once but not alone? +
Filter Keys or a similar setting is ignoring single presses. Turn it off under Accessibility settings.
Can a keyboard shortcut disable part of the keyboard? +
Yes. Fn lock changes the function row, Num Lock changes the numpad or the overlay, and game mode on gaming keyboards disables specific keys. None of them are faults.
Do keys fail in groups when a keyboard is dying? +
Often. Membrane keyboards lose keys along a row or column as a trace corrodes. Mechanical keyboards lose keys one at a time as individual switches wear.