Instructions for notebooks:
1. Disconnect all external devices you have.
2. Unplug the power adapter from the notebook.
3. Remove the battery from the notebook (if possible).
4. Press the power button and hold it for at least 15 seconds.
5. Reconnect the power adapter.
Do not yet reconnect the external devices, they should stay disconnected. Do not yet reseat the battery.
6. Switch your computer on and test if it boots normally and watch if the power LED lights up.
7. If the power LED still does not lights up, continue with the next steps.
8. Disconnect the power adapter from the notebook.
9. Press the power button and hold it for at least 15 seconds.
10. Reseat the battery. Do not reconnect the power adapter.
11. Switch your computer on and test if it boots normally.
Instead of 15seconds. Try holding the power button for 1 minutes at least.
And try it for both without adapter once and without battery once...