HP Probook 440 G3

So I recently got a HP Probook 440 G3 from a friend which did not power on at all and now I'm trying to fix it. I've already tried the following:

- Reseating the RAM

- Static discharge before powering the laptop on

- Removing the battery and using directly from the power source

- Replacing the CMOS battery

- Looking at the motherboard for any burn marks

None of them has worked so far. The odd thing is that when I reset the CMOS battery, it powers on but then upon next shutdown, it has the same issue as before.

Any advice on how I can identify and fix the problem? Thanks in advance!

Also, note that I do not have access to repair equipment such as a soldering iron or a voltmeter.