Diagnosis
This is a frequent handshake bug with the monitor's power-saving mode and certain graphics cards or cable types. The monitor goes into a deep sleep and doesn't respond to the wake signal.
How to Fix It
First, try a different cable, preferably a high-quality DisplayPort cable if you're not already using one. DP often has a more reliable wake signal than HDMI on this model. If that doesn't help, disable the monitor's deep sleep. In the OSD, go to 'Setup' -> 'Power Saving' and set it to 'Off'. This will use slightly more power when the PC is off, but it prevents the deep sleep state that causes the hang.
If That Didn't Work
The issue can be driver-related. Update your graphics card drivers. Also, in Windows, go to Power Options -> Change plan settings -> Change advanced power settings. Expand 'PCI Express' -> 'Link State Power Management' and set it to 'Off'. This prevents the GPU from powering down the port too aggressively.
Heads Up
With 'Power Saving' off, the monitor's standby LED will remain a solid white instead of blinking when your PC is off. Don't be alarmed—that's normal.