Screen doesn't work at all? You get no picture?
Please try External monitor see if you get picture on external monitor, if you don't get picture, try pressing down the FN button together with one of the F1-F12 buttons, one of them will swap the display from the internal to the external.
If you still don't get picture at all the laptop is not starting up, this is most of the time caused by a hardware failure, are you in warranty?
You can try reseating the memory modules on the laptop, remove the battery and power adapter, turn the laptop upside down, unscrew the memory cover, remove the memory modules.
Remove both modules, then turn the laptop over, plug in the power adapter and try turning on the laptop, it may beep, it wont start up, let it run for 1 minute, then unplug power.
turn the laptop over and insert the other ram module into the other slot, turn the laptop over and try starting up again, does the laptop start up?
If it does not start up, unplug power, turn over, remove ram module, place it in other slot, try turning on, if it still does not work. Repeat steps with other memory module.
If the laptop still does not start up, reinsert memory modules and close the cover, mainboard or video adapter is possibly faulty.
contact hp for warranty or out of warranty repair.
We can not repair failed motherboard or video adapter at home, video adapter is build into mainboard most of the time, not fixable at home.