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A flickering screen is hard to ignore. Even subtle flicker can cause eye strain, headaches and fatigue, and obvious flashing makes a computer almost unusable. The causes range from a loose cable or wrong refresh rate to driver problems and, occasionally, failing hardware. The fix depends on which one you have, so the first job is to observe the flicker carefully.

Ask yourself a few questions. Does the whole screen flicker, or only certain parts? Does it happen all the time, only in certain apps, or only at certain brightness levels? Does it happen during startup, before Windows or macOS loads? The answers point you towards the right fix much faster than trying random solutions.

Here is a simple diagnostic. If only part of the screen flickers, such as the taskbar or one window, the cause is almost always software. If the whole screen flickers, including in the BIOS or startup screen before the operating system loads, the cause is almost always hardware: the cable, the connection or the display itself.

On Windows, Microsoft suggests opening Task Manager while the flicker is happening. If Task Manager flickers along with everything else, suspect the display driver. If Task Manager stays steady while other things flicker, an app is likely the cause. It is a quick way to narrow things down.

You can also run our display test in full screen with a solid colour. Solid colours make flicker, banding and brightness pulsing easy to see, and they remove any app from the equation.

For external monitors, the cable is the first suspect. HDMI and DisplayPort cables can be damaged internally, and low quality or very long cables may not handle high resolutions and refresh rates reliably. Push the cable in firmly at both ends. Try a different cable, and if possible, a different port on the computer and the monitor.

Adapters and docks add another point of failure. USB-C to HDMI adapters and docking stations are frequent causes of flicker, especially at 4K or high refresh rates. Test by connecting the monitor directly if you can. If the flicker disappears, the adapter or dock is at fault or needs a firmware update.

• Use a certified cable rated for your resolution and refresh rate.
• Avoid very long cables without active signal boosting.
• Keep display cables away from power cables where possible.
• Update the firmware of your docking station.

Monitors are designed for specific refresh rates, such as 60, 120, 144 or 165 hertz. If the computer sends an unsupported or unstable refresh rate, the screen may flicker or go black briefly. On Windows, open Settings, System, Display, Advanced display, and choose a refresh rate listed for your monitor. On a Mac, System Settings, Displays, Refresh rate.

Variable refresh rate technologies like FreeSync and G-Sync are great for gaming but can cause flicker in some games, menus or at low frame rates, especially on certain VA panels. If flicker happens mostly in games or when frame rates dip, try disabling variable refresh as a test.

Graphics drivers are a very common cause of flicker on Windows, particularly after updates. Download the latest driver directly from Intel, AMD or NVIDIA, or from your laptop manufacturer's support page, which sometimes has drivers tuned for your model. If flicker started right after a driver update, roll back to the previous version using Device Manager, Display adapters, Properties, Driver, Roll back driver.

For a stubborn case, a clean driver installation can help. Some graphics vendors offer a clean install option in their installer, which removes old settings before installing fresh ones. On a Mac, graphics drivers are part of macOS, so installing the latest system update is the equivalent step.

Some screens control brightness by rapidly switching the backlight on and off, a technique called pulse width modulation, or PWM. At lower brightness levels, the switching becomes slower and some people notice flicker or feel eye strain, even if they cannot see it directly. OLED phones and laptops often use PWM at low brightness.

If your eyes feel tired at low brightness but fine at higher levels, PWM may be the reason. Try keeping brightness higher and reducing the room's darkness contrast with a lamp. Some devices offer a flicker reduction or DC dimming option. When buying a new monitor, look for flicker-free or PWM-free models if you are sensitive.

If only certain windows flicker, look at recently installed or updated apps. Older antivirus programs, screen recording tools, and apps with their own display overlays can conflict with the operating system. Browsers with hardware acceleration occasionally flicker with certain drivers; try toggling hardware acceleration in the browser settings.

Uninstall recently added software one at a time, or start Windows in safe mode. If the flicker disappears in safe mode, a driver or startup app is the likely cause.

If the screen flickers during startup, in the BIOS, or in every mode, and the cable and connection are fine, hardware may be failing. On laptops, flicker that changes when you move the lid often indicates a damaged display cable in the hinge, which is a common wear point. On external monitors, a failing backlight or power board can cause flicker that gets worse over time or as the monitor warms up.

Connect the laptop to an external monitor as a test. If the external monitor is stable, the laptop's internal display or cable is the problem. If both flicker, the graphics hardware may be at fault. Check your warranty, as display and graphics faults are commonly covered.

1. Observe: whole screen or part, all the time or in certain apps.
2. Run the full screen display test with solid colours.
3. Reseat or replace the cable and try another port.
4. Set a supported refresh rate and test without variable refresh.
5. Update or roll back graphics drivers.
6. Adjust brightness and turn off adaptive brightness features.
7. Test with another monitor or device to isolate hardware.

Following these steps in order solves most flicker without spending money. If you do need a repair, you will know exactly which part is at fault, which helps avoid unnecessary replacements.

Phones and tablets can flicker too, especially at very low brightness, after a drop, or following a software update. Turn off adaptive brightness and any extra dim or reduce white point feature as a test, then restart the device. If flicker appears only in one app, update or reinstall that app. If it happens everywhere and gets worse when you press the screen gently, the display connector or panel may be damaged and needs professional repair.

For external displays connected to laptops, try a different graphics mode. Some laptops switch between integrated and dedicated graphics, and flicker can appear only on one of them. The graphics control panel usually lets you choose which processor handles each app.

TVs used as monitors deserve a special mention. Many TVs apply motion smoothing, dynamic contrast and energy saving modes that can cause pulsing or flicker with computer signals. Switching the TV input to PC or Game mode disables most of this processing and usually produces a stable, sharper picture with lower input lag.

Not every flicker comes from the computer. Fluorescent lights and cheap LED bulbs can flicker at frequencies that interact with the screen refresh, creating a shimmering effect that looks like a display fault, especially on camera. Try changing the room lighting or turning it off to see whether the flicker disappears.

Power quality matters too. A monitor sharing a power strip with a heater, air conditioner or other heavy appliance may flicker when that appliance switches on. Plug the monitor into a different outlet or use a surge protector. On laptops, a faulty or non-original charger can sometimes cause brightness pulsing, so test on battery power and with the original charger.

Strong magnetic fields from large speakers or subwoofers placed right next to a monitor rarely affect modern screens, but they can interfere with nearby cables. Keeping display cables tidy and away from power bricks is a small, free improvement worth making.