Hi @SofiaM15  POST works, which says no hardware problem detected, but unable to Boot into Windows operating system. Please keep trying to Boot into Windows, on the fourth attempt the Windows recovery window will open so that you can repair the Windows operating system. Be sure to select option that does not erase all of your personal files. 

You should have created a standby OS(C:) boot drive as part of your disaster Recovery Plan, now is the time to swap this in to get your m15 R3 up and running within minutes. 

Hi @SofiaM15  Your computer can be non-responsive because of one of the following reasons: No Power, No POST, No Boot into Windows, No Screen. Please see if Dell Article Number 000179529 provides a fix for your No Boot into Windows. Thank you. 

Thank you, but it didn't turn on... just the lights in the keyboard, I'll try it so many times and it didn't changed.

Hi @SofiaM15 try LCD built-in self-test (BIST) diagnostic to get test pattern on screen. Look at screen obliquely (at an angle) to see if very faint screen image is present, which then indicates screen backlight has failed. Backlight is part of screen, so replacement screen is required. 

I try it but I just watched a white flash in the screen and nothing else

Thank you, but i try it but it didn't show anything

Hi @SofiaM15  we have undertaken the necessary diagnostic tests to confirm that the screen's cable is not connected or the screen has failed and requires replacement.