Hp dv will not start up

itz may b caused frm many internal hardware cause, like the battery(main/cmos); ram; sm section of the system board; ccfl; inverter circuit; or even the lcd....

howevr, before proceeding to complex test to verify the current status of ur laptop, at 1st all u need is to put on the laptop to charge for atleast 4hrs..(the gauge status may show u a pseudo process)..
if u r a professional, remove the ram(s) from itz slot(s), gently rub itz connector teeth using a rubber to remove carbon or oxide formed if any..
connect it to a external monitor n see if display is coming..
check the internal system battery to b above +3v..

so itz always better to hv supervision..frm ur system admin/vendor/good or authorized service center....