Hi @usubaka ,
It probably won’t work but try starting the tablet in safe mode and check if there is a display.
If no good then try shining a torch at an angle close to the screen when the tablet has been turned on and check if you can detect any images at all.
They will be very faint so trying this in a darkened room may help to see them if they are there at all.
If there are images there then there is a backlight problem.
Since you have replaced the screen then most probably it is in the motherboard's backlight power supply circuit.
I can't find the schematics for the motherboard but with a lot of phones/tablets there is a fuse in the circuit so perhaps it has blown for whatever reason.
If there are no images on the screen when using the torch then there is a problem with the systemboard. Has the tablet been dropped or gotten wet at all?