What are the possible reasons if the laptop doesn't show display but you can see indicator lights are blinking, HDD and CPU fan are working?

Most likely there are two scenarios.

1. Problem with the LCD, which would require a replacement of the screen unit.

2. Problem in the connection cable between the motherboard and LCD. If it is a simple contact issue, it can resolved by opening the laptop case and reattaching the cable properly. If the cable is damaged, it has to be replaced.

In either cases it is advised to have it handled by someone with expertise, to avoid the risk of further damage. If under warranty, best to sent it over to an authorised service centre.

Hello,

1- Connect your Laptop through the VGA into an LCD screen, it should show the screen over LCD (to be sure that your VGA is 100% working and has no problems.

2-If the above step is working, Continue and disassemble the laptop and screen cover , check if the cable between the Motherboard and the screen is connected probably  .

3-if its connected well, then you need to replace the whole screen because you cannot change the flat cable without changing the screen.

4-If your VGA has a problem, you would have to actuly just buy another laptop because the VGA is a built-in and cant be changed too. unless you change the whole motherboard.

In My views best practice to  troubleshoot the issue .First off all Plugged External LCD through laptop external VGA port and  power up laptop . It should clear LCD screen from mind doubt.move the flip down and up to see any life of flex cable.    Then Ram Must be checked by replacing it .if not then Issue is in laptop motherboard It must be Reset by removing cmos battery .press power button for 30 second with put battery and power .

Step1. Remove battery and remove power supply Step 2. Hold down power button without power supply for about 1min Step3. Plug in you power cable and push you power botton Screen should come on at this point Step 4. Put back your battery and continue If this doesn't work, maybe your screen is bad or your connectors is having problem.

Do not replace the LCD Screen first.. this is much expensive.. 1st wash the RAMS of your laptop, it is possible there is RAM issue.. 

Check the ribbon cable that goes from the laptop to your display, it is a very common problem

You can fiw it by yourself, open the screen frame carfeully (use a small screw driver) and also open the cover beside the keyboard and there you can see a flat cable cross the2 units.

Check for scratch or if the cable is cut, if it is the case then, remove it carefully and buy a new one from specialized spare part shop.