DIAGNOSIS That's a classic sign of the monitor losing sync with the signal, often due to a cable issue, a dodgy connection, or an aggressive power-saving feature.
FIX First, check and reseat all your cables—power, HDMI/DP/USB-C—at both ends. The primary culprit is usually a slightly loose or failing video cable. Try a different, high-quality cable. Then, go into the monitor's OSD (joystick menu) and navigate to Display > Power Savings. Turn this setting OFF. This feature can sometimes be too sensitive and misinterpret a static image as no signal.
IF THAT DIDN'T WORK The issue might be on the source side. Update your graphics card drivers. For NVIDIA users, also try disabling any adaptive sync/G-Sync Compatible settings in the NVIDIA Control Panel for this monitor, as the handshake can sometimes cause brief dropouts.
HEADS UP If you're using a cheap HDMI switch, KVM, or dock, that's a likely point of failure. Try connecting the monitor directly to your computer to rule out intermediary devices.