Black Screens

Hello everyone! I have a problem that made me turn from a passive reader to registered member here.

I have a 4GB RAM/64GB eMMC LP Version S70CR110/S70CR100 Z8300 -> V1.0

It used to work fine with Windows 10 and the 7 inch IPS Panel connected via the flatflex ribbon cable and a 3A PSU. I then tried to update the bios to the auto-boot version and experienced this:
 

I followed the steps to prepare the thumbdrive following the description.I did not connect another display via HDMI.On start I did not see the Bios update screen, that I expected. In fact the display remained totally black.After a while I turned off the power and tried to reboot with the thumbdrive disconnected and the display still remained black.I conected another display via HDMI and didn't get a picture either.I checked the external display and HDMI cable wit another device -> both work fineI tried to do serveral hard resets following the description without success.I tried to follow this instruction for a blind recovery with no hdmi output without success. No picture and the keyboard doesn't even blink.Trying to flash the default bios blindly din't work either.

Symptoms wenn connecting to PSU

blue led blinks a few times and turns offred led turns on and stays on.

The only thing I haven't tried is flashing the Bios chip with a programmer. Because I don't have one. Any ideas to solve this issue?