Why does my laptop power light flash 3 times but not turn on?

I have a hp pavilion notebook 15-au181na laptop. When I push the power button the light by the place where you plug in the laptop charger flashes 3 times but does not turn on.

It all started when I was trying to reinstall windows 10 using a USB. This is because I had to replace my laptop bottom case and keyboard because the old ones were cracked and I had to remove the mother board, battery and hard drive and then put them back in. When I did this then the computer would not boot up and therefore I had to reinstall windows 10 using Rufus and a USB.

I have tried removing the battery and then pushing the power bottom for 30 seconds however, it has not worked. I also tried plugging in the power without the battery and this also has not worked.

Does anyone know why my laptop will not turn on?

Thank you if you can help.