It's one of two things:  a  bad display, or a bad backlight power supply.  A shop can likely diagnose further, or you can start replacing parts (display panel first;  if that doesn't solve the issue, replace the system board).  
It started off as a processor fan not working, changed that, Battery didn't take any charge, changed that, after all of this the laptop still doesn't show display while the laptop is turned on with a full battery and functional fan. (I know the battery has some charge because before when it didn't take charge when I unplugged the laptop while it was charging it turned off.)
My Inspiron 13z 7359 turns on but with no display