HI,
When unit powers on, are you able to hear windows booting sound.
Check for the CAPS LED status as well. Is it steady or blinking?.
If it's blinking
Kindly refer to this link
http://h10025.www1.hp.com/ewfrf/wc/document?cc=us&lc=en&docname=c01443366
If caps LED is working normally then it Might be the issue with the Display Panel.
You Can Contact hp Technical Support and get this properly diagosed.
I am an hp Employee.