Monitor With No Image: Black Screen, No Signal, Flicker or Shutdown

You press the computer's power button, hear it boot, but the monitor stays blank — either fully black or with "No Signal" in a corner. Sometimes the image appears for a second and vanishes after a few minutes; sometimes the screen flickers and shuts off. Before you assume the monitor is dead, it's worth a few minutes to isolate which part is at fault: power, backlight, signal or cable.

At the service bench we diagnose monitors in exactly that order — power first, then backlight, then signal. You can do most of these steps at home without opening the case, and they alone will tell you whether a cable swap is enough or the device really needs to come in for diagnostics. This article walks through the six most typical scenarios on Dell, LG, Samsung, AOC, BenQ, Philips and Asus monitors.

No LED lights up at all — the power side

Start with the simplest check: does the monitor have power at all? Look at the power indicator — the small LED on the front bezel or underneath. If it doesn't light up at all, the problem is in the power circuit, not the image.

• Check the external power supply. Many monitors (especially Dell, LG, AOC) use an external adapter — that black "brick" on the cable. It usually has its own small LED. If that LED is dark, the adapter is at fault, not the monitor.
• Try a different outlet. In older Riga apartment blocks, evening voltage dips are not rare, and some power supplies simply won't start at borderline voltage. Plug the monitor straight into a wall outlet rather than an extension lead.
• Check the power cord. On monitors with internal power (no external "brick"), it is usually the input socket and the fuse on the power board that take the load.

If the adapter's LED is on but the monitor still shows no LED at all, the problem is in the internal power board — most often a swollen capacitor or a fuse blown after a voltage spike. That is service work: replacing components on the board itself, not the adapter.

Indicator on, screen black — backlight or board

This is the trickiest scenario. The power LED is on (or changes from orange to white when you connect the computer), you hear the monitor "wake up", but the screen stays black. Most of the time this means the image is actually there — there's just nothing to light it up, because the backlight has failed.

Run the same flashlight test we use for televisions:

1. Leave the monitor on and connected to a computer that is outputting an image.
2. Darken the room.
3. Hold a bright flashlight (a phone torch works) right against the screen and look at it at an angle.

• If you can make out the image in the faint light — the desktop, icons, the mouse cursor — the panel and signal are fine, but the backlight (LED strips or their driver) has burned out. This is repairable: the backlight LEDs or the power/backlight board are replaced.
• If there's nothing under the flashlight — just solid black — then either the panel or the main board has failed. This one needs diagnostics with the case open.

The flashlight test separates a simpler backlight repair from a more serious board problem in a couple of seconds, which is why it is the most valuable step on the whole list.

No Signal — cable, input and graphics card

If the screen isn't black but shows a floating "No Signal" message (or "Check Cable", "No Input"), the monitor itself is alive — it simply isn't receiving an image from the computer. The culprit is almost always outside the monitor.

Work through the checks in this order:

1. The right input. Press the monitor's Input / Source button and switch to the socket the cable is actually plugged into — HDMI 1, HDMI 2, DisplayPort or USB-C. Very often the monitor is waiting for a signal on the wrong input.
2. Check the cable at both ends. Unplug and firmly reseat the HDMI/DisplayPort cable on both the monitor and the computer side. A DisplayPort plug often has a latch that stops it seating fully.
3. Swap the cable. A crimped or cheap cable is a frequent offender. If you can, try another cable or another standard (for example HDMI instead of DisplayPort).
4. Check the computer side. Plug the cable into the graphics card output, not the motherboard output (if the computer has a separate graphics card, the motherboard HDMI is often disabled). If the monitor works with another computer or a laptop, the fault is in your computer or its graphics card, not the monitor.

If "No Signal" appears even when the monitor is connected to a known-good computer with a known-good cable on the right input, then the problem is in the monitor's input board — and that's what we check at the service centre.

Image flickers or vanishes after warming up (capacitors)

This is the classic monitor failure, and you recognise it by its signature: the device works while cold but starts limping once it warms up. Typical signs:

• The monitor turns on with a delay — you press the button and the image only appears after several tries or after a minute.
• The screen displays normally for a few minutes, then starts flickering and shuts off, but the LED stays lit.
• After cooling down, the whole cycle repeats from the start.

Almost always the cause is swollen capacitors on the power board. Electrolytic capacitors dry out and swell over the years, with their top bulging or even splitting. In heat their capacitance drops, the voltage "sags", and the board protects itself by shutting down. In damp Riga flats and after voltage spikes this progresses faster.

This is readily repairable: the swollen capacitors are replaced with new ones of the correct capacitance and voltage rating. But it is soldering on the power board, where dangerously charged capacitors remain even after unplugging — not something to do at home. If you see this "warm-up" signature, bring the monitor in before the board damages other components.

Stripes, dim light or the flashlight test for the backlight

Some symptoms don't remove the image entirely but clearly point to the backlight or panel side:

• Uniformly dim image — everything is visible but very dark, even with brightness at maximum. Some of the backlight LEDs have burned out, and the rest only partially light the screen.
• A pinkish or dark band along the screen edge — often unevenness in the backlight or its driver.
• Thin coloured vertical or horizontal stripes — usually a panel ribbon or T-Con contact problem, not the backlight.
• A crack or "ink" blotch — physical panel damage; the panel has to be replaced, and that rarely pays off on a monitor.

This table links the symptom to its most likely cause and what to do next:

The line between DIY and the service centre is simple: anything that doesn't require opening the case — input, cable, outlet, the flashlight test, switching off and on — is safe to do at home. Anything involving soldering, capacitors, backlight LEDs or board components is service work, because dangerous voltage remains in the power board.

Is the monitor worth repairing or replacing?

Unlike a television, a monitor's fault is far more often on the power or backlight side than in the panel itself — and those are exactly the parts that repair well. The decision is guided by the assessed cause and the device's age (monitors are typically used for 4–6 years):

A general rule of thumb: if the monitor is a good one (IPS, high resolution, large diagonal or a professional model) and the fault is in power or backlight, repair is almost always sensible. If it's a cheap, long-used panel with physical damage, replacing it usually makes more sense. Only an inspection settles it for sure: we run a quick on-site diagnostic, pin down which part has really failed, and tell you honestly whether the repair is worth it.

We diagnose and repair monitors from Dell, LG, Samsung, AOC, BenQ, Philips, Asus and other brands. If you'd like to read about the same flashlight logic in a television context, the article on how to tell a burned-out backlight from a damaged matrix is useful, while all monitor and TV faults are gathered on our TV and monitor repair page.