Why the screen of my pc is white and not working

Did you drop it?

This symptom may also indicate a virus, the deaded "FBI" virus, which may also claim to be from DHS, Justice Department, or whatever. Occasionally this malware breaks and doesn't work properly, leaving the user with a white screen.

Try restarting in safe mode command prompt. (Hit F8 as the BIOS screen flashes past and select that option)

If it starts up normally in that safe mode, then you have a virus. If the screen is still white you probably have a broken LCD.