V1 SX Core, 3.0.3 beta, screen is black

[Ryo]

I've just installed SX Core and was trying to install SX OS
I've got green light, SX OS menu
I've confirmed SX Core update and it seemed to work. I've generated license request file, went back and started NAND backup

At about 1% screen turned black and I can't seem to turn Switch on anymore

Sometimes there is green LED, sometimes there is nothing when I try powering it ON

I've disassembled it too casing, detached and re-attached battery, same with SD card slot - no difference

Currently I've left it charging

What would be my next steps to try? Or is it dead?

 

[Grimlock97]

When there is nothing happening when you press the power button, try to press the power on button for 20 seconds. Then press again once the power on button.
I would also check the nand connection. See if all connections (NAND chip plugged to modchip, one connection from modchip to the nand connection of motherboard) were well plugged and the flex cable connector from the soldered cable is also well plugged.