Inspiron 7566 wont post

Hello. 

My Inspiron 15 7566 is stuck on the Dell logo (it won't post). 

Indicator (LED light) does nothing and no sound error can be heard. 

What I tried so far: 

- Removing all the peripherials and memory devices

- Removing both SSDs

- Removed the battery and the CMOS battery. BIOS restarted but the issue is still there. 

- I removed 1 stick ram tried it in both slots and the same with the other. - no solution

- I disassembled the laptop - tried it without a keyboard, without touchpad, without left USB IO, without a wireless adapter. 

At this point I am lost. Any help will be appreciated. 

side note: once I reassembled the laptop, it once booted and detected the changes in memory. But when I instructed to reboot to BIOS again, it got stuck again.