Water damaged laptop, replaced motherboard but it still doesn't work

[JebLab]

I'm trying to repair a laptop that had water spilled on it. It won't boot at all.

I replaced the motherboard with a working one, but it still won't boot. 

The only signal I get from the computer is an amber flashing light when I plug it in via charger.

How do I fix this?

[WAWood]

@JebLab 

Hard drives are sealed, so there is no way for water to get into them, but the electrical contacts are not, and if water touched those, it's possible the drive controller got shorted out, and if that happened, the drive will simply not spin up.

You should consider running the built-in hardware diagnostics to see which devices, if any, have failed.

You do that by pressing the Esc key repeatedly while rebooting the PC.

Eventually, you should the the HP Startup Menu that looks something like the one below:

When that appears, press the key indicated for running System Diagnostics -- and report back here what it finds.

[JebLab]

Tried that, but I am unable to reboot the computer. The power button doesn't do anything along with the rest of the keyboard.