It is important to know why in specific situation our laptop is not working. This information is important because helps the user when he calls the mechanics to describe what exactly the problem is and saves time and efforts of the both sides.  What may the problem be if:
Laptop does not switch
This means that your laptop is not reacting on the turn on button pressing, the ventilator is not turning or the problem is in the lights. The indication for the battery can light but can be passive as well. Reason for those can be a lot, like:
•    The stabilized rectifier or the so called adapter is defective, the battery is off, is defective, or is missing. If you press the turn on button and battery light is on but laptop is not starting maybe the problem is powerless battery or the problem is with the power.
•    Bad or missing contact in the adaptor, of the power in the plate or interrupted cable.
•    Damaged or missing record on BIOS.
•    Defective element in the power block on the plate. In this case you can be sure it is either defective integral scheme or of the power, defective power cascade and etc.
•    Electric problems in one of the bridges

The laptop has no initialization in turning on
This means that when you press the switching button for turning on, the ventilator starts spinning and does not stop, the turn over is high, the indicators are lighting but they do not turn off, forward  loading is missing, there is nothing on the screen. What causes this? May be the processor and the memory are missing of there is defective record on the BIO or the north bridge is not working.

Laptop turns off on initialization of BIOS stage
It must de separated from operative system not loading. It can be caused of:
•    Over heating of the south bridge
•    Over hearing of the processor because of dust in the radiator or the ventilator or bad contacting cooling. This problem is not permanent.
•    Power is missing and the battery is off. The laptop tries to take power from the battery but as it is empty, the laptop turns off.
•    Problem with the BIOS.

Not recognizing the hard disk
You surely can enter the BIOS. This defect has different deeds depending on the laptop. Some systems stop while entering the BIOS after which there is black screen and massage for non systemic disk can appear. Can be caused of defective hard disk, defective north bridge or bad contact.

Display is not working
The defect can be of the picture, there is not picture at all, there is picture but it can be barely seen. Causes can be:
•    Partly or fully defective graphic processor, bad contact of the integral scheme, problem with the memories.
•    The micro key
•    Band cable of the display
•    Inventor of the display
•    Problem with display lamp
Battery is not charging
This can be because of defect on the battery, defect on the charging block of the plate, there is not enough power on the external charging.

Check this list every time you have problem with the laptop and you need to call mechanic.