DIAGNOSIS The monitor is powered but not receiving a valid video signal from your GPU. The most common cause is an incorrect input source selection on the monitor.
FIX Use the monitor's joystick button to manually select the correct input. Press the joystick to open the menu. Navigate to Input. Select the port your cable is connected to (e.g., DisplayPort 1). Do not rely on auto-detect. If using DisplayPort, ensure the cable is fully seated at both ends. The connector clicks when secure.
IF THAT DIDN'T WORK The GPU driver or output resolution may be incompatible. Boot the PC into Safe Mode. Connect the monitor. Install or update the GPU driver from NVIDIA or AMD. Restart. Also, try setting the PC's output resolution to 1920x1080 @ 60Hz via another display first, then reconnect the 27GN950-B.
HEADS UP The monitor's DisplayPort firmware is known to have handshake issues with some GPUs. LG released a firmware update (file name typically '27GN950_27GN950B_VerXX.XX.exe') to address this. You must install it via the OnScreen Control software on a working system.