If the screen does show a self-test OK, but there's no image internally or externally, the mainboard needs to be replaced.  If you need a part reference, post the full system model number - Inspiron 3593, 3501, etc.

@ejn63​ but laptop starts but display is off, no black screen, and model is pp39l and 1558 

, tell me the problem which is occurred

I am facing an issue with my Dell Inspiron 1558

- Internal screen does not turn on during normal boot.

- Colour test / backlight works fine.

- LCD cable, port, and LVDS signal line are working correctly.

- 1 RAM stick may be faulty; HDD is old.

- Beep codes are not coming during boot.

- External monitor works fine (optional if you tested).

What could be the reason for the internal screen not showing display? Is this a motherboard / EC issue? Please advise possible fixes or repair options.

Thank you.

No one can confirm the exact fault without access to the system, but a failed GPU is top of the list.  Bear in mind the system is worth about $20 at most -- it can be replaced for far less than a repair will cost.

https://www.ebay.com/p/131629117

@ejn63​ what are the symptoms of failed gpu?

Prime one would be no display at all.

@ejn63​ wait gpu is not dead bcz laptop  screen worked for like 6 days in past before again coming to this problem.

It isn't uncommon for intermittent failure before complete failure.  

You can take the system to a repair shop for their evaluation, but the diagnostic fee is likely to be 4-5 times what the system is worth.

Well I will suggest you to checkout the following thread: https://www.dell.com/support/contents/en-us/article/product-support/self-support-knowledgebase/monitor-screen-video/laptop-display-screen-not-working

1. Power & Display Toggle

• Restart the laptop fully.

• Press Fn + F8 (or the key with a monitor icon) to cycle through display modes — internal only, external only, both.

If Screen Is Completely Black

2. External Monitor Test

• Connect your laptop to an external monitor or TV via HDMI/DisplayPort/VGA.

• If the external screen works, the issue is likely with the internal display, cable, or connector.

3. Brightness & Keyboard

• Try increasing brightness using the brightness keys (often Fn + F11/F12 or arrow keys).

• This can be overlooked if brightness got turned all the way down.

Software & Driver Fixes

4. Safe Mode or BIOS Check

• Restart and press F2 (or Delete) immediately to enter BIOS.

  • If BIOS screen shows, the hardware is likely okay — it’s a software/driver issue.

  • If BIOS doesn’t show, it points toward a hardware/display panel problem.

5. Update or Reinstall Display Drivers

If you can see anything on screen (or via external monitor):

1. Right-click Start → Device Manager

2. Expand Display adapters

3. Right-click the GPU → Update driver

4. Or Uninstall driver and restart (Windows will reinstall automatically)

6. Windows Display Settings

• Go to Settings → System → Display

• Check that “Multiple displays” isn’t set to Second screen only