HP Probook 450 G4 wont power on even when Plugged in

[Mjoslin]

HELP!! One of my coworkers is reporting that his HP Probook 450 G4 is no longer powering on. Even while plugged in the power will not come on. The power button also feels like it is not engaging. (There is no clicking) What could it likely be? The battery or the Power button? I know how to replace the battery.. but not the power button.. computer is currently taken apart to remove battery. 

[CherylG]

If you plug in the adapter without the battery does it power on? 

Removal/Replace videos are here:

http://h20574.www2.hp.com/results.htm?SID=5224999&MEID=C989BFC0-04C0-4AA5-849F-80E221323919

[Mjoslin]

I'm not sure, as the whole computer is apart to remove the battery. 

[CherylG]

I thought the Probook has removeable battery- slide latch to release?

[Mjoslin]

Not the G4 version, you have to open the whole computer to remove it. 

[CherylG]

Maintenance and Service Manual shows power button replacement:

http://h10032.www1.hp.com/ctg/Manual/c05270979

Or-video here:

http://h20574.www2.hp.com/results.htm?SID=5224999&MEID=C989BFC0-04C0-4AA5-849F-80E221323919

[FirstMetroSecIT]

Battry couldve drained due to hibernation. Plugin the power adapter, then press the power button for 20 seconds. White light will be visible for a second from the adapter port, release the power button. Now press the power button to turn it on.

[VietHuynh]

It's started!

Thank you.

[kipketer]

FirstMetroSecIT´s solution (holding the power button for more than 20 seconds) helped me. Thank you!