Windows Doesn't Recognise a Second Monitor: How to Fix It
The two checks almost everyone overlooks (input source, projection mode) before touching drivers.
You connect a second monitor and Windows acts like it doesn't exist — black screen, or it doesn't even show up as an option. Before suspecting drivers or cables, there are two very simple checks that get overlooked more often than it seems.
1. The monitor's own input source
Many monitors have several inputs (HDMI 1, HDMI 2, DisplayPort...) and don't switch automatically to the one in use. If your monitor is showing "HDMI 1" but you connected the cable to "HDMI 2", you'll see a black screen even though everything is physically connected fine. Look for the "Source" or "Input" button on the monitor itself and confirm it's on the correct input.
2. Windows' projection mode
Press Windows + P — a menu opens with 4 options: "PC
screen only", "Duplicate", "Extend" and "Second screen only". If it's
on "PC screen only", Windows doesn't even try to use the second
monitor, even though it's physically connected and detected. Choose
"Extend" or "Duplicate" depending on what you need.
Force detection
Settings → System → Display → "Detect".
Try another cable and port
HDMI/DisplayPort cables come loose more easily than it seems.
Update the graphics driver
From the manufacturer's website (NVIDIA, AMD, Intel), not just Windows Update.
If it suddenly stopped working (it worked fine before)
This points to a recent change — a graphics driver update is the most common cause. If the problem started right after updating, try reverting to the previous driver version from Device Manager → your graphics card → Properties → "Roll Back Driver".
Tip: before ruling out the monitor entirely, try it on another computer (or on your TV, using the remote to switch source). If it doesn't show a picture there either, the problem is with the monitor, not Windows.
If the problem is only with high resolutions (4K)
An older port or cable might not have enough bandwidth for 4K, causing exactly the same "not detected" symptom. If your monitor is 4K and the cable is several years old, trying a newer cable (certified for the resolution you need) fixes this more often than people think.
Frequently asked questions
Why does the monitor only work if I connect it alone, not with the others at the same time?
It could be because the graphics card is close to its bandwidth limit with several monitors at once, especially at high resolutions. Try lowering the resolution on one of the monitors to check.
Do I need to install drivers to connect a second monitor?
Usually not, it's plug-and-play. You only need to touch drivers if the monitor isn't detected correctly despite being connected properly and having the right input source selected.
How do I know if the problem is with the monitor or my PC?
Try the monitor on another device (another PC, a player, your TV). If it doesn't show a picture there either, the problem is with the monitor itself, not Windows.