If you already tried the:
1) battery trick
and
2) Copy everything off the SD card, reformat it in [ FAT32 | 32 KB cluster size | MBR disk | Primary Partition ] with MiniTool Partition Wizard, full Write + Verify tested it empty with H2testw (scanned for hardware defects), and attempt booting the o3DS with SafeB9SInstaller renamed as boot.firm and Luma3DS v7.0.5 (arm9loaderhax.bin, in case you have older CFW),
you may need to disassemble o3DS and check if the WiFi module has popped off. Be careful as there are flex cables (especially shoulder buttons) that can be easily ripped when removing the shell.
Other than that, try looking for signs of activity through
Recovery Mode,
Luma3DS chainloader (START), and
Luma3DS v9.1 configuration (SELECT) when turning it on.