Why isn't my Laptop coming on?

@ruthfelix the troubleshooting for issues like the one you describe all require the same beginning. Check these things first.

First 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 a 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. Use this guide for that

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.

To work on our laptop use the HP ProBook 640 G1 Maintenance And Service Guide

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