HP ProBook 6470b Notebook not powering on or showing any signs of life

@yikess this is going to be tough since it does have a history of water damage. Start all the usual things first. I am aware you may already have tried most of this but it is helpful to get to a common starting line.

Start off with the easy things. Disconnect the power from the computer by unplugging the power cord from your computer. Disconnect all external devices from the computer. Now hold the power button depressed for about 30sec-1min. Reapply the AC power adapter and see if your computer does show any sign of life.

Next you want to check your power supply. Make sure it has the proper voltages. Check to make sure that connectors are not bend etc. Check the DC-in jack of your laptop. Make sure there is no corrosion, debris etc. that prevents it from working. Clean it of any debris etc. use a few puffs of air to clean it out. If none of this works, get an ammeter and see if your laptop draws any amperage from the charger. After that, you need to check and see if your motherboard even gets power. For that of course, you need to open it up. Post Some good pictures of what you see. That way we can see what you see. Adding images to an existing question

It is also possible that this is a bad RAM module or a bad LCD. So remove the RAM, clean the contacts with a pencil eraser. Do it gentle so as to not destroy the module. Replace it and restart. If you have more than one module, remove it and just leave one connected.

We will need to know your computers exact model number. It will also be helpful if we can see the motherboard (both sides). Make sure that you post images that are well focused and large enough so we can zoom in to identify possible issues.

Let us know how things are working out with each check/test.