Lenovo B50-80 won't boot, backlight flickering

[HighwayStar89]

Hi to all,
I have this laptop that suddendly won't boot.
When I plug the power adapter, the charging LED turns on.
When I press the power button, I can hear the fan spinning, and the screen start flashings, with the frontal green LED flashing too.
No other vital signs.
I reseated the RAM, changed the RAM, changed CMOS battery, disassembled, cleaned, and reassembled all the boards, changed thermal paste and reflowed, tried the NOVO button (the tiny reset button on the right side) to enter BIOS, tried F2 or Fn + F2, changed power adapter, but with no luck.
I think the BIOS is corrupted, but I'm asking here, hoping someone had the same situation and can help.
Here is a video of the problem:
Lenovo B50-80 screen flickering no boot

Thank you all

[evilgenius31]

You can try flashing with a EEPROM programmer - but to me, it looks more like a hardware issue.

If you connect it to an external display, do you see anything?

[HighwayStar89]

Thank you evilgenius31, connected with an external monitor I have no signal. I think the problem is the motherboard, I supposed the BIOS because it is the first thing the system load up at boot.
Anyway, can you please suggest me a programmer? Thanks

[evilgenius31]

I use a CH341A. You’ll want one of the new ones with adjustable voltage.