Fix: When the Second Display Stays Dark
Practical checklist for the always-confusing "no signal" message on a perfectly good monitor.
Cable, Port, Source — Always First
Try a different cable. Try a different port on the system. Try a different input on the monitor. Two of these three are nearly always the cause when "no signal" appears on a monitor that worked yesterday.
For Hdmi, downgrading from a 4K-rated cable to a known-good Hdmi 1.4 cable temporarily isolates whether bandwidth is the problem.
The Operating System Side
Open the display settings panel and click "Detect" — the operating system sometimes does not notice a monitor that was connected after boot. If detection succeeds, the monitor is fine and the previous failure was a hot-plug issue.
Check the resolution and refresh rate set for the second monitor. A rate the monitor cannot accept causes the same "no signal" message a bad cable would. Drop to a safer combination first, then ramp up.
When the Driver Side Is Suspect
Update the graphics driver from the card maker's download page. Many "no signal" cases on second displays trace back to a driver that does not yet support a specific monitor or hub.
For laptops with discrete graphics, confirm which output port is wired to which graphics chip. Some ports are wired only to the integrated chip, which may not be active in the current power profile.
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