hp pavilion dv4 black screen but the cap and num lock blink

First, try a Hard Reset as follows.

Shut down the notebook, unplug the AC Adapter and then remove the battery.  Hold  down the Power button for a full minute.  Re-insert the battery, plug in the AC Adapter and see if the notebook will start.

If it still doesn't start, is there a sequence to the 'blinks' that you can match to the table below?

http://h30434.www3.hp.com/t5/Notebook-Operating-Systems-e-g-Windows-8-and-Software/my-hp-pavilion-dv4-screen-wont-turn-on-but-the-cap-and-num/td-p/1009127

http://www.insidemylaptop.com/disassemble-hp-pavilion-dv4-laptop/