Dead or stuck pixels are the most common reason a brand-new monitor gets returned. A dead pixel is permanently black; a stuck pixel shows one fixed color. Both are easy to spot when you know how.
The simplest test is to fill your screen with each primary color — white, black, red, green, blue — and look closely. Any dot that doesn't change with the background is a defect.
BlankPane makes this easy: open the tool, tap each color tile to go full screen, and scan the display. Repeat for red, green, and blue to catch every kind of stuck subpixel.
What to do next: most manufacturers replace panels with a few dead pixels within the warranty window. If the pixel is stuck rather than dead, a quick pixel-exercise animation sometimes revives it.