"No signal" on the second screen? Work through cables, inputs, adapters, and display settings.
Moderate⏱ 10–30 minWindowsMac
A second monitor that shows "No signal" or never appears in display settings is almost always a connection problem rather than a broken screen. The cable, the adapter, the monitor's selected input, or the port on the laptop is the usual culprit.
USB-C adds an extra wrinkle: not every USB-C port carries video, and not every USB-C cable supports it. Checking what your ports can actually do saves a lot of frustration.
Try these first — 30 seconds each
[ ]Make sure the monitor is on and set to the right input (HDMI 1, HDMI 2, DisplayPort, USB-C) using its menu buttons.
[ ]Unplug the video cable at both ends and reconnect it firmly.
[ ]Try a different cable — video cables fail more often than monitors do.
The full fix
6 steps in the order that solves it fastest, plus platform notes, prevention, and when to call
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1
Ask the computer to look for displays
Windows: Settings → System → Display → Multiple displays → Detect. You can also press Windows key + P and choose "Extend" or "Duplicate". Mac: System Settings → Displays; if the monitor is missing, hold the Option key to reveal a "Detect Displays" button.
2
Check the port and adapter
For USB-C or Thunderbolt, look for a lightning bolt or DisplayPort (D-shaped) symbol next to the port — ports with neither may be data or charging only. Adapters and docks are frequent failure points; if you have one, try connecting the monitor directly, or try another adapter.
3
Rule out the cable and monitor
Connect the monitor to a different device, like a games console or another laptop. If it works there, the problem is on the computer side. If it does not, try another cable before assuming the monitor is faulty.
4
Update the graphics driver (Windows)
Open Windows Update → Advanced options → Optional updates for driver updates, or download the latest driver from Intel, AMD, or NVIDIA (or your laptop maker). You can also press Windows + Ctrl + Shift + B, which restarts the graphics driver — the screen flickers briefly.
5
Check the resolution and refresh rate
If the monitor is detected but the picture is black, scrambled, or flickering, the computer may be sending a resolution or refresh rate the monitor or cable cannot handle. In display settings, pick the monitor, then choose its recommended resolution and a 60 Hz refresh rate to test.
6
Check how many displays your computer supports
Some laptops — including base-model Apple silicon MacBook Air and MacBook Pro models from recent generations — only support one external display natively. If a second external screen will not appear, check your model's specifications on the manufacturer's website.
Platform notes
Windows
If the monitor worked before a Windows update, try rolling the graphics driver back: Device Manager → Display adapters → right-click → Properties → Driver → Roll Back Driver.
Mac
Macs that go to sleep with a monitor attached sometimes do not wake it. Unplugging and replugging the cable, or closing and reopening the lid, usually brings it back.
Stop it happening again
Buy cables rated for the resolution and refresh rate you use (for example, HDMI 2.0 or 2.1 for 4K at 60 Hz or higher).
Label which dock ports support video.
Avoid bending cables sharply at the plug.
When to get professional help
If no external display works on any port with known-good cables, the computer's video output or port may be damaged. If the monitor fails on every device, contact the monitor manufacturer about warranty repair.
This is general troubleshooting information for home users. Menus and settings differ between
device models and software versions. Back up important data before making changes, and contact
the manufacturer or an authorised repair provider for hardware faults or anything under
warranty.
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