Fix a Second Monitor That Isn't Detected
The monitor says “No signal”, or your computer acts like it isn't there. Work through these fixes in order. Most of the time it's the input setting or the cable.
Check the monitor's input setting
Monitors with more than one port (HDMI 1, HDMI 2, DisplayPort, USB-C) only show one at a time. Use the buttons on the monitor, usually on the bottom edge or back, to open its menu and pick Input or Source, then choose the port your cable is plugged into.
While you're there, make sure the monitor's power light is on and it's plugged in at the wall.
FIXTry these in order
Open a step, try it, then tell us if it worked.
- Unplug the cable at both ends and push it back in firmly. HDMI and DisplayPort cables often look connected but aren't.
- Try a different cable if you have one. Cheap or very long cables fail more than you'd expect.
- Try a different port on the computer.
- Desktop PC: plug the monitor into the graphics card (the ports lower down on the back, usually in a horizontal row), not the ports near the USB sockets. If you have a graphics card, the upper ones often don't work.
Press Win P and choose Extend. If “PC screen only” was selected, Windows was ignoring the monitor.
Still nothing? Go to Settings › System › Display › Multiple displays and click Detect.
Open System Settings › Displays. If the monitor isn't shown, hold down the Option key; on recent macOS versions a Detect Displays button appears. Click it.
Also try putting the Mac to sleep for a few seconds (Apple menu › Sleep) and waking it, which makes it check connections again.
Press Win Ctrl Shift B. The screen flickers and you hear a beep as Windows restarts the graphics driver. If that doesn't help, restart the computer with the monitor plugged in and switched on.
Restart the Mac with the monitor plugged in and switched on. The Mac detects displays as it starts up.
- Plug the monitor directly into the computer to rule out the adapter or dock.
- USB-C: not every USB-C port can send video. Look for a small DisplayPort (D-shaped) or Thunderbolt (lightning bolt) symbol next to the port, or check your laptop's specs.
- Docking stations: many need the dock maker's driver installed first, especially docks that use “DisplayLink”. Check the dock's support page.
- Check your Mac's display limit. MacBooks with a base M1 or M2 chip support only one external display. See the FAQ below.
First install everything in Settings › Windows Update, including Optional updates, where driver updates often appear.
For the newest driver, get it from your graphics maker. To see which you have, search Device Manager and expand Display adapters:
- Intel → Intel Driver & Support Assistant
- NVIDIA → NVIDIA drivers
- AMD → AMD drivers
Did it stop working right after an update? In Device Manager, right-click the adapter › Properties › Driver › Roll Back Driver.
Display support is built into macOS, so updates often fix monitor problems. Install anything in System Settings › General › Software Update, then restart.
Connect the monitor, with the same cable, to another computer, laptop or games console.
- Works elsewhere: the monitor and cable are fine; the problem is your computer's port, adapter or settings.
- Doesn't work anywhere: try another cable once more. If it still fails, the monitor likely needs repair or replacement; check its warranty.
- The computer's video port may be faulty. A USB-C video adapter or a dock can be a cheap workaround.
- Contact your computer maker's support with the model number; some laptops need a firmware (BIOS) update for external displays.
FAQCommon questions
Why does my monitor say “No signal”?
The monitor is on, but it isn't receiving a picture on the input it's set to. Check the input source first, then the cable and port. If the computer is asleep, move the mouse to wake it.
Why can't my MacBook use two external monitors?
It depends on the chip. MacBooks with a base M1 or M2 chip support one external display. A MacBook Air with M3 supports two, but only with the lid closed. M4 and newer MacBook Air models support two with the lid open. Pro and Max chips support more. Apple's pages below list every model.
Can I use an HDMI splitter to add a second monitor?
No. A splitter sends the same picture to both screens; it can't extend your desktop. To get two separate screens from one port, use a docking station or a USB-C adapter that supports multiple displays.
The monitor is detected but the picture is blurry or the wrong size.
Open Display settings, select the monitor and choose the recommended resolution. If text looks too small or large, change the Scale (Windows) or choose a different resolution option (Mac).
My mouse moves to the wrong side of the screen. How do I fix that?
In Display settings, drag the screen boxes so they match how the monitors sit on your desk. On a Mac you can also drag the white menu bar to choose the main display.
My laptop has one HDMI port. Can I still connect two monitors?
Usually, if the laptop also has a USB-C or Thunderbolt port that supports video. Connect one monitor to HDMI and the other through a USB-C video adapter, or use a dock.