The laptop has to video on the external monitor connected to the VGA port. The laptop screen works fine.
1. External monitor turned off.
2. Wrong settings.
3. Bad VGA cable or bad connection.
4. Bad VGA port on the laptop.
Possible troubleshooting steps and repair solution:
1. Make sure the external monitor is turned on.
2. The laptop is set to output video only on the internal screen. On most laptops, you can switch video output between internal and external screens using a keyboard shortcut. You hold down the Fn key and at the same time press one of the F keys. This shortcut is different for different brands.
For Toshiba laptops use: Fn+F5
For HP laptops use: Fn+F5
For IBM/Lenovo laptops use: Fn+F7
For Dell laptops use: Fn+F8
Some other brands may have different shortcuts.
Connect the external monitor to the laptop, make sure the monitor is turned on, and use one of the above-mentioned shortcuts to switch video from internal to the external mode or set the laptop to display on both screens. The video output depends on how many times you press on the F key.
In some brands, you can enable or disable output on the external screen in the BIOS settings. Enter the BIOS menu and search for the video output settings in there.
3. Try reconnecting the VGA cable connecting the laptop and monitor. The cable could be defective. Try replacing the cable.
4. There is a slight chance that the VGA port on your laptop is defective. In this case, you’ll have to replace the VGA board or motherboard, it depends on the model of your laptop.