Question Asus S551L not starting

Sep 19, 2019
recently I tried to repair a broken hinge on my girlfriend's laptop. Everything seemed to be fine unless I tried to power on the laptop. I was quite confident I can do the repair without any problems, as I repaired a few laptops before. Seems I was wrong.

When I plugged the laptop in, the only thing that would happen was the power button light turned on for a moment, then it turned off and the orange LED, near a "battery" symbol turned on after another second.
When I pressed the power button again, the process would repeat. White power light flashed, the orange LED turned off and after a second turned on orange again.
I couldn't hear fan nor HDD starting to spin during the process.

A change happened when I tried to reset the CMOS battery by disconnecting it for about 10 minutes (while having the AC and battery cable unplugged).
After connecting the AC again, it seemed like the laptop was actually trying to start now, but only for about 2 or 3 seconds, then turned off again and the process repeated. It seemed like with every failed attempt, it would try for a little bit longer, eventually the HDD started to spin for a second and turned off again. This process has repeated multiple times.
Usually after about 10-15 unsuccessful bootlooped tries it turned off completely and to make the process repeat, I had to reset the CMOS again.

I tried a different AC adapter to check whether it could be it's fault. But the behavior remained the same. After returning to the original AC adapter, the laptop doesn't do anything at all.
Not even the power led flashes, no sounds, nothing.

I tried running it without the LVSD, without batter, without HDD, without ODD, CMOS, combination of all of these at once. But nothing seemed to do a change.

I came back to it today, nothing has changed. So I decided to write here.
I hope I didn't break any rules of this forum. Tried searching for solutions but all failed.
I tried to provide as much detail as possible. If any more details are needed, I can provide them.