Hi @dan2014 ,
Try a power refresh and check if that resolves the problem.
* Disconnect the charger if connected and then remove the battery from the laptop.
* Press and hold the laptop's Power On button for a ''full 30 seconds'' and then release it.
* Reinsert the battery, reconnect the charger and check if it turns on.
If still no good you may have to remove/replace the RTC battery from the systemboard as well and check if doing that fixes it.
Here's the [http://h10032.www1.hp.com/ctg/Manual/c04763947.pdf|maintenance and service guide] for the laptop that may help.
Go to p.57 to view the necessary pre-requisite steps and then the procedure to remove/replace the RTC battery.
I'm not sure that you have to remove the systemboard as I think that the battery should be visible once you can access the systemboard.
Once you have removed the RTC battery, measure its voltage. It is a 3V Lithium battery and usually lasts about 5-6 years. If it is <2.5V DC, replace it. Search online for ''697917-001'' to get results for suppliers that suit you best.
Reinsert the RTC battery (or its replacement), reassemble the laptop, reinsert the main battery, connect the charger and check if it turns on.