Laptop is dead. How to troubleshoot.

Example 1. The computer is absolutely dead. 

When you plug in the AC adapter and press on the power button, there are no signs of life at all. It appears to be dead.
What you can do ?
1. Make sure the wall outlet is working and the AC adapter is getting power from the outlet. Try another wall outlet.
2. Test the AC adapter, make sure the voltage output is correct. You can test the adapter with a voltmeter.
3. If the adapter is good, try reconnecting the battery. Remove the battery, wait for 1-2 minutes, plug in the adapter and try turning it on again.

If the adapter doesn’t pass the test with a voltmeter, replace it with a new one and test the computer. I always recommend buying an original replacement adapter from the manufacturer, not a generic one.
There could be more than one adapter available for your model.
The voltage output on your new adapter must be exactly the same as on the old one. The amperage, on the other hand, can be the same or higher.
If previous troubleshooting steps didn’t help, it’s possible your computer has a problem with the motherboard or DC power jack. In this case it’s necessary to disassemble the laptop and test the DC jack.

Example 2. The computer turns on and makes normal startup noises, the LED lights turn on but noting appears on the screen.

First of all, take a closer look at the screen under bright light. It’s possible the screen shows the image but it’s very faint. In this case you’ll have to troubleshoot the backlight failure.
On the other hand, if the screen shows no image at all, test the laptop with an external monitor (or TV) connected to the VGA port or DVI port or HDMI port.
You can toggle video output between internal and external modes by using Fn keys:
– Fn and F4 keys simultaneously on HP laptops
– Fn and F5 keys on Toshiba laptops
– Fn and F7 keys on IBM laptops.
Other laptops may use different key combinations.

If the external monitor works fine but the internal screen has no image at all, the problem can be related to:
– Poor connection between the video cable and screen or motherboard. Try reconnecting the video cable on both ends and check out if this helps.
– The screen failed. Replace it with a new one.
– The video cable failed. Replace it with a new one.
– The motherboard failed.

If both, the internal and external monitors show no image, the problem can be related to:
– Failed memory (RAM).
– Failed motherboard.

– Try reconnecting the memory module, maybe it’s not making good connection with the slot.
– Try cleaning contacts on the memory module.
– Try moving the memory module into another slot.
– Try replacing the memory module with another one.
If you have two modules installed you can try removing them one by one, it’s possible that one of the modules failed. Try moving modules from one slot to another.
If changing or reseating memory doesn’t help, you can try this:
Removing the battery, hard drive, DVD drive and other components you can easily access. Try turning on the laptop without these components installed.
It’s possible one of them failed and it’s preventing the entire computer from starting up properly.

Also, try turning on the laptop with an external monitor while the video cable is unplugged from the motherboard.
If external image appears after you disconnected the video cable, apparently there is something wrong with the cable. Replace it with a new one.

If the computer is still dead, try removing other internal components (wireless card, modem, keyboard, etc…) and test it with an external monitor after each removed part.

The last step is testing the laptop as a barebone system.

On this picture you see my final test. The motherboard has been removed from the base and I assembled a basic barebone system on my bench.
The bare bone system includes:
1. Motherboard (like in most cases it has onboard graphics chip).
2. CPU with the cooling module.
3. Known good memory module.
4. The power button board.
5. Known good AC adapter.
If the system still doesn’t turn on, it’s either bad motherboard or failed CPU.
If you computer shows garbled or distorted image, check out this post.

source:- laptoprepair101