Thank you.

I found that Esc key is not working on the laptop's  built-in keyboard.

I tried resetting my BIOS but i cant get into the panel that comes when i press F2. I can see that panel actually comes, but just for about half a second.. I think the Esc key is triggering,right? (I cant get to the motherboard jumper or the CMOS battery)  

I downloaded the BIOS for the system from dell.. After clicking 'start to flash' a windows with squares comes, and restarts. Tell me whether there is a part of installation after the restart. For me the installation did not continue after restart.  

Is there a way to disable the built-in keyboard for a while?

Just to let you know that today i was pressing different keys and i got into ePSA Pre-boot System Assessment and i passed all the tests.

Sorry for my bad english

Its the Esc key which is making all the problems. Its always pressed.

So any idea to fix the Key? or how to disable the built-in keyboard and use another USB keyboard?

Remove it from the mainboard. See the Owners Manual:

http://ftp1.dell.com/Pages/Manuals/inspiron-14-intel-n4050.html

here is a post from another user

'You must have an internal keyboard in place or the system will not complete POST'

so if i remove the built-in keyboard the system wont boot??? (i dont know what POST means)

Remove the keyboard and see if you can loosen the esc key, you can probably remove the esc key to avoid it being pressed down if you are careful.