DIAGNOSIS This is a classic 'no signal' scenario. The monitor is getting power, but it's not receiving a valid video signal from your computer, so it just shows a blank screen.
FIX First, check the source. Press the button on the monitor (usually the one under the bottom bezel) to open the OSD menu. Navigate to 'Input Select' and make sure it's set to the correct port you're using (like HDMI 1 or HDMI 2). If that's right, the issue is likely the cable or port. 1) Power everything off. 2) Unplug the HDMI or DisplayPort cable from both the monitor and your PC. 3) Check the ports for any bent pins or debris. 4) Plug the cable back in firmly on both ends, then power everything back on, starting with the monitor.
IF THAT DIDN'T WORK Try a different cable if you have one, even an old VGA cable as a test. Also, try plugging the monitor into a different video output on your PC, like a different HDMI port on your graphics card or even the motherboard port, to rule out a dead PC port.
HEADS UP If you're using a desktop with a dedicated graphics card, your cable must be plugged into the card's ports (usually lower on the case), not the motherboard's ports. Plugging into the motherboard will often give you a black screen if a card is installed.