Power button board

Hello,
First I would like to thank everyone who reads this post. It's amazing to me that there are guys kind enough to help people like me solve their computer problems free of charge.

Now I recently replaced the screen on my laptop and was putting it back together when I decided to test it to see if it is still working. I had everything connected except for the keyboard and battery. When when I hit the power button, I got nothing. So I thought I should check the power button board first, and I saw that when I jiggled the ribbon cable, the powerbutton lights up for a bit and the fan starts moving but after a few seconds it turns back off again. So I got a new power button board and I got the same result. What am I doing wrong? Is it a ribbon cable port issue, the power button board, or some distant problem on the motherboard?

Laptop: a 6-year-old HP pavilion notebook laptop.
Model Number: 15-n066us
Modifications: 3 years into its life I upgraded to an SSD, and it worked for the 3 years before I tackled the screen (replaced with identical screen).

Thanks again guys!