1. Check whether the monitor is connected to the laptop via HDMI/DisplayPort/VGA cable correctly.

2. Check and make sure that your laptop’s video output is enabled.:

3. Make sure that you laptop's display settings are correct.

4. Restart Your Laptop and External Monitor.

5. Update or download the latest graphics card driver for your laptop.

6. Connect your laptop to another display device and check if it works.

7. Consult your laptop manual for any additional instructions.