HP EliteBook boots but screen stays blank

Hi.

I got a problem with my EliteBook - it boots (I hear the sound of Windows coming up), but the screen stays black from the moment I press the power button (it lights up, just doesn't show anything). I can even play with the brightness of the screen after windows is booted (I see the light goes up or down when I play with it), but it stays that way.

I tried the method of pulling out the battery and then holding down the power button for 60 seconds, and powering the laptop with only power adapter (no battery) at first, but it doesn't work. Also I tried the method of holding down the windows key + B key and then powering up the laptop but still not luck.

Any suggestions?

Thanks