If you have two monitors connected and only one of them is currently working, please try swapping the connection cables between the monitors to see if this makes a difference. This is usually the easiest way to troubleshoot if there is an issue with the connection cables. Alternatively, try swapping the ports the monitors are connected to or try them on a different device. Some devices such as Apple M1 and M2 systems have a monitor limit of one external display, a docking station or monitor that bypasses this limit will work however they usually require drivers. Ensure that they are up to date and installed properly, and reconnect the monitors or restart your computer. If the monitor does not turn on in any way, contact the manufacturer for further assistance.