Diagnosis
The monitor is getting power but isn't receiving a valid video signal, or it's stuck in a standby/input detection loop. This happens a lot with the auto-source switching.
How to Fix It
First, unplug the monitor from the wall for a full minute. While it's off, check that your DisplayPort or HDMI cable is firmly plugged into both the monitor and your PC or console. Reconnect the power. If the screen is still black, press the joystick button on the back to open the OSD. Navigate to the source menu and manually select the correct input (like DP or HDMI 1) instead of leaving it on 'Auto'.
If That Didn't Work
Try a different, known-good video cable. The G6 is finicky with some older or low-quality cables, especially for high refresh rates.
Heads Up
If you're using a PC, sometimes the graphics driver crashes and doesn't output signal. A full PC restart (not just sleep/wake) while the monitor is on can force a fresh handshake.