Some Dell OptiPlex computers natively support dual monitors, either by supplying two monitor connectors or a Y-adapter that allows two monitors on one line. Power off your computer and monitors.

Apart from inspecting the cable, make sure the HDMI ports on both your PC and the Dell monitor are fine without any damage or dust that hinders the proper connection. If you have used a VGA cable ...

Dell is pitching the monitor for use in retail or warehouse ... there’s an HDMI 1.4 port and DisplayPort 1.2 connector, plus three USB-A ports, an additional USB-C downstream port, audio line ...