HDMI “No Signal” errors on Windows 10 and Windows 11 are usually fixed by checking the cable, selecting the correct monitor input, bypassing docks or adapters, changing Windows projection mode, forcing display detection, resetting the graphics driver, or reinstalling display and USB drivers...
Windows 11 users whose second monitor is not detected should first verify the physical display chain, then use Windows + P, Settings > System > Display > Multiple displays > Detect, and graphics-driver troubleshooting to separate a bad cable, dock, adapter, driver, power state, or hardware limit...