Keyboard Keys Not Working
A dead key, a sticky key and a ghosted key are three different faults. The test tells them apart in about a minute.
Open the Keyboard Tester, press Start testing, and work along every row. A key that never lights is dead or taken by your system; a key that stays lit after you let go is sticking; keys that disappear when you hold several at once are ghosting, which Logitech describes as normal on membrane keyboards when three or more keys are pressed together. Cleaning helps sticky keys: Apple's own instructions are compressed air, a 75-degree angle, a left-to-right sweep, straw half an inch away, and never inverting the can.
“My keyboard is broken” covers at least four different problems, and they have different answers. Before buying anything, find out which one you have.
One minute with the tester
Open the Keyboard Tester, press Start testing, and work along each row in turn, watching the drawn key light up as you press it. Then hold a few keys down together and watch the counter.
| What you see | What it usually is |
|---|---|
| The key never lights | Dead switch, or a key your system takes before the browser sees it |
| It lights only when pressed hard or in one corner | Dirt, or a worn contact under that key |
| It stays lit after you let go | A sticking key: the release was never reported |
| Held keys vanish when you add a third | Ghosting, which is a limit of the keyboard rather than a fault |
| The wrong character appears | The layout your system is set to, not the hardware |
A key that does nothing in one program and works in another was never the keyboard's fault.
The key that does nothing
Check it somewhere else first. A browser only receives the keys your operating system passes on, so media keys, brightness keys, some Fn combinations and any shortcut the system claims for itself can be invisible to a web page while working perfectly. Open a text editor and try the same key there.
If it is dead everywhere, the next question is whether it is dirt or the switch. Try the key with a firm, square press in the middle. A key that works when pressed dead center and fails at the edge is usually debris rather than a failed switch.
The sticky key
In the tester, a sticking key is unmistakable: it stays lit after your finger leaves it, because the browser was told the key went down and never told it came up. That is the one fault where cleaning has a real chance of fixing the problem.
Apple publishes a specific routine for its own notebooks, and it is a sensible pattern for any keyboard:
- 1
Hold the machine at a 75-degree angle, "so it's not quite vertical".
- 2
Spray compressed air across the keyboard, or just the affected keys, in a left-to-right motion, then repeat with the machine turned to the right side and to the left side.
- 3
Use the straw that comes with the can to control the airflow, keeping its end about half an inch from the keyboard.
- 4
Do not invert the can while spraying. That sends propellant rather than air onto the keys.
Check your own maker’s page before you start: a desktop mechanical keyboard, a laptop and a membrane board are different objects, and the maker’s routine is the one that keeps the warranty intact.
Keys that vanish: ghosting and rollover
This is the fault people mistake for a broken keyboard most often, because nothing is broken at all.
Logitech’s description is exact: when certain multiple keys, “usually three or more”, are pressed at the same time, “not all of the keystrokes will appear and one or more may disappear (ghosted)”. The reason it happens on membrane keyboards is that “the activation is made between the membrane surface and circuit board”. Logitech also notes the useful exception: two modifier keys, such as Ctrl and Shift, together with one regular key should still work as expected.
The Keyboard Tester’s “Most at once” counter is where you see your own limit. Hold two keys, then three, then four, and watch the number stop climbing. Games are where this bites: hold a direction and a modifier, press a third key, and the one you needed is the one that disappears.
No general number is given here, because the limit belongs to your keyboard rather than to keyboards in general. Measure your own; it takes ten seconds, and it is the only figure that applies to you.
When it really is the hardware
If a key is dead in every program, survives a clean, and behaves the same on another computer, the switch under it has failed. On a desktop keyboard with removable switches that is a cheap repair; on a laptop it usually means a keyboard assembly, which is a job for the maker or a repair shop.
Before you get that far, the Mouse Tester is worth a minute too if the trouble started at the same time as something else odd: a failing USB port or hub can produce symptoms on both devices at once, and Logitech’s own advice for input faults includes trying a different port without a hub.
Questions
A key does nothing at all. Is it broken?
Not necessarily. A browser only sees keys the operating system passes on, so media keys, some Fn combinations and shortcuts your system claims may never reach the page. Check the same key in a text editor before blaming the keyboard.
Why do keys disappear when I hold three at once?
That is ghosting. Logitech's explanation is that when three or more keys are pressed simultaneously "not all of the keystrokes will appear and one or more may disappear", and that membrane keyboards are susceptible because the activation is made between the membrane surface and the circuit board. Two modifier keys plus one regular key should still work.
How do I clean a sticky key safely?
Apple's instructions for its notebooks are specific: hold the machine at a 75-degree angle, spray compressed air across the keyboard or the affected keys in a left-to-right motion, keep the straw about half an inch away, and do not invert the can while spraying. Other makers publish similar routines for their own hardware.
The key types the wrong character. Is that a fault?
Almost never. That is the keyboard layout your system is set to, not the hardware. The tester shows both what the browser calls the physical key and what it types, so a mismatch between them points straight at the layout setting.
Is a repeating key the same as a sticky key?
They look alike and are not the same. A sticking key stays lit in the tester after you release it, because the release was never reported. A key that repeats while held is usually the system's own key-repeat setting doing exactly what it was told.
How this guide was made
The ghosting explanation and the cleaning instructions are quoted from the manufacturer support pages listed below, with the date each was read. The testing procedure is what ScreenTail's own Keyboard Tester does, described from the tool as it is built.
No rollover number. How many keys a particular keyboard can report at once is a property of that model, and no general figure could be sourced, so the guide shows you how to measure your own instead. No disassembly instructions either: pulling keycaps and prising out switches is beyond what a web guide should talk anyone through.
- 01What keystroke ghosting is, that it appears when three or more keys are pressed simultaneously, why membrane keyboards are susceptible, and the modifier exception: Logitech, Keystroke ghosting on Logitech membrane keyboards — retrieved Sep 23, 2026.
- 02Cleaning a keyboard with compressed air: the 75-degree angle, the left-to-right spray, the straw distance and the warning not to invert the can: Apple, How to clean the keyboard of your MacBook or MacBook Pro — retrieved Sep 23, 2026.