If you hold the Select button while turning it on, it should show the Luma3DS configuration screen.
You might want to delete /luma/config.bin to reset the configuration as well. Also run CHKDSK on the SD card in case there's any corruption, and/or try another card if possible.
You might want to delete /luma/config.bin to reset the configuration as well. Also run CHKDSK on the SD card in case there's any corruption, and/or try another card if possible.