This article explains how to test your computer monitor to see if it is working properly. This process can take anywhere from a few minutes to much longer, depending on the cause of the problem

To test your monitor, follow these simple troubleshooting steps:

Check if it's on! Some monitors have more than one power button or switch. Check if they're all on.

Check if the monitor power cables are loose. Your monitor may be working fine and your only problem may be a loose or disconnected power cable.