The Problem

Windows is running—you can see the desktop on the laptop or primary screen—but a second monitor shows "Didn't detect another display" or No signal. If every screen is black from power-on (no BIOS), use black screen on boot instead.

The Fix

Step 1: Tell Windows to Extend

Win + P → Extend. Settings → System → Display → Detect → Identify to match monitor numbers.

Step 2: Cable, Port, Input

Plug into the GPU rear ports on desktops, not the motherboard (unless you use CPU graphics only).
Monitor on the correct HDMI / DP input.
Try another cable—cheap HDMI fails at high resolution.
USB-C video needs DisplayPort Alt Mode, not a charge-only port.

Step 3: GPU Driver

Device Manager → Display adapters → update from NVIDIA / AMD / Intel (or laptop OEM). Issue started after an update? Roll back driver.

Step 4: Ghost Monitors

Unplug externals → Device Manager → View → Show hidden devices → Monitors → uninstall grayed entries → reconnect → reboot.

Step 5: Docks and Laptops

Update dock firmware and Thunderbolt/USB4 drivers. Use the USB-C port with the monitor icon. Plug in AC power—some laptops disable external GPU output on battery.

Step 6: Hybrid Graphics

NVIDIA Optimus: NVIDIA Control Panel → set external display to discrete GPU if video only works on the internal panel.

Hardware vs Software

Monitor works on another PC or a console? Cable, dock, or panel fault. Only this PC fails? Stay on drivers and Display settings.

How to Fix a Second Monitor Not Detected in Windows 11