HP Probook won't boot up.

Thank you in advance for anyone who can help.  I have a laptop that my niece was given, and she has used for a year or so. It stopped working and they sent it my way.  Based on the issue and the LED above the power jack I surmised that the system board was faulty.  I ordered a replacement off eBay and after making the swap I am getting the same issue.  The unit will not boot.  I get a single white LED flash when the power supply is connected.  8 amber flashes when the power button is pressed. 

Specs: HP Probook 4525s with apparent water damage inside the case. (One reason I started with the system board, plus the lights code from the power jack and a quick google search.)

Troubleshooting:  I have tested the power supply with an OHM meter.  Removed the previous system board part# 613211-001 and replaced with one that I was assured came from a working unit. *Fingers crossed that is right.* I have removed the battery pack, hard drive, wifi module and the optical drive to try to get it to boot to BIOS. Replaced the CMOS Battery.

 Any advice is appreciated. 

try removing battery and power cord, then hold the power button down for 30 seconds.  then plug power back in and see if it boots. if it does then plug the battery back in.

Edited by mightywiz, 04 April 2018 - 04:59 PM.

Removed the Battery pack, and the power supply.  Held the power button for 30 seconds.  Same result. 

White single flash when power is connected. 8 amber flashes.  Thanks for the feed back. 

Which LED is blinking 8 times?

Since you say there was water damage, have you tried turning it on with the keyboard disconnected?

Edited by DavisMcCarn, 05 April 2018 - 07:58 AM.

DavisMcCarn you are the tech of the day!  If this site gives out gold stars then you get one from me!  Removed the mouse and keyboard.  The thing fired right up when power was applied, and started playing a video almost immediately (even before login)  Off to find a mouse now. The keyboard is fine.

And the LED is right above the where the power port plugs in on the right side.

Edited by XtraKargo, 05 April 2018 - 09:45 PM.

The original IBM PC specs allow the keyboard port to be used for loading diagnostics (for one thing) and a stuck key on the keyboard can wreak havoc on the PC's booting.  I'm glad that was it!