I will start by describing my problem that due to Pook I solved.
My laptop will start and the screen does not light up at all, no sound, the power button will just stay an, no blinking. I realized that the system was not booting, but had no clue due to why. Then after applying some pressure aver the laptop on the part of the hard drive, the laptop started up normally. SOLUTION: i opened the HD compartment, and got it out, and the putted back in, and screwed more tight the screws (be carefull to not screw them to much, just a little bit more then normally), this was my first time opening and getting out the HD, and I found a small spring on on the hard facing upwards, and putted the same back in.
Now to give some ideas for the other problems:
-if the display won`t open at all, no sounds, the power button is just staying on and if the system is not booting, the it my be the HD like in my case;
-if the display is lighted and is only showing a black screen, then it could be the display inverter;
-if the display is not opening and you hear the system booting (hint try hitting enter or try to give it a restart (CTRL+ALT+DEL) to confirm booting), in this case it is indicated to try connecting a monitor to the laptop an if that works then it is the display or maybe the display inverter.
These are some tips that I hope will be useful.
P.S: Thanks Pook for your advice !!!