Hacking Help: my 3DS can ONLY be used with 4.5 FW. Others FW don't work

[Keylogger]

Hi,

I have a problem with my 3DS XL...

I don't know why but I can only use it with the 4.5 FW.
If I upgrade the console, it will not boot (black screen)

I have a USB NAND Mod so I can write my 4.5 NAND back but if i write any 4.5+ NAND (for ex my 9.2 NAND) the console will not boot.

I have updated from 4.5 to 8.0 with smash bros retail game and now the 3DS doesn't boot so I have to write my 4.5 NAND back...

Do you know what it the problem?

Thanks a lot

EDIT: sorry wrong section