You’ve connected your laptop to an external monitor, but no image is displayed on the external screen. What would be the main cause of that issue?

use the fn keys to switch On display and cross check with cables and driver support

It may be cable Fault or The screen Resolution Diffrence

Normally when you connect an external monitor to a laptop running Microsoft Windows, the laptop automatically detects a multi monitor setup and therefore pops a list of options of how you want to use the monitor:

- Laptop Screen only.

- External Monitor only.

- Duplicate the output on both screens.

- Extend the content on both screens.

If the list is not automatically displayed, you can use the (FN) key on the keyboard with the combination of another key (EX: FN + F5 on a TOSHIBA laptop).

The external monitor may not be able to display the content IF:

1- Not connected to a power source.

2- Not turned on.

3- Not properly connected (The cable is damaged, The input port of the monitor is damaged, or the output port on the laptop is damaged) 

4- Display drivers not installed and configured properly.

5- Output resolution/ refresh-rate is not supported.

6- Laptop's operating system problem.

7- Multiscreen option is disabled in the BIOS (if supported) 

when connecting an external monitor; and if the image is not automatically displayed on this monitor, we can use the Fn key + the Fonction key (from f1 to f12) to switch display . 

But the problem here is the key associated to switch display is differnet from a laptop model to another; so the easiest way will be the universal keys combination: Windows key + P , option that we will get are:

1/ Display the internal monitor only,

2/ Display only projector

3/ Extend the display

4/ Duplicate both screens

If this is not possible after doing this manipulation, there are two causes: 

1/ the graphic driver is not properly installed (graphic accelerator is missing or deriver is corrupted)

2/ The graphic card is defected (external port that we use may also be damaged , it can be VGA DVI HDMI )

There is a button in your laptop called Function (Fn) hold it and find another button in Functions buttons your will find drawing of two items monitor and laptop> Some laptops working with ctrl or shift it depends

You need to Right Click on Desktop then go to Screen Resolution (Windows7) or Properties (Windows XP) then select your display. On Windows7 you can select for the image to be displayed on both Monitors or just on the External Monitor (in which case you can set your maximum resolution to whatever the External Display is able to use, bypassing the laptop's screen resolution limitation)

AT FIRST WE NEED TO CHECK THE NETWORK PROPERTIES THEN CHECK CABLE IF THE CABLE IS WORKING FINE THEN WE NEED TO CHECK THE NIC THROUGH COMMAND "PING127.0.0.1" IF IT WORKING FINE THEN OS WHETHER THE OS IS NOT CURRUPTED.