With a bit of luck, this should be an easy fix. Try clearing HOME menu extdata + theme data
# Power off your console
# Insert your SD card into your computer
# Navigate to the ``/Nintendo 3DS/<ID0>/<ID1>/extdata/00000000/`` folder on your SD card
# Delete the corresponding folder for your 3DS region:
** ***EUR Region***: ``00000098``
** ***JPN Region***: ``00000082``
** ***USA Region***: ``0000008f``
** ***CHN Region***: ``000000A1``
** ***KOR Region***: ``000000A9``
** ***TWN Region***: ``000000B1``
# Delete the other corresponding folder for your 3DS region:
** ***EUR Region***: ``000002ce``
** ***JPN Region***: ``000002cc``
** ***USA Region***: ``000002cd``
# Reinsert your SD card into your console
In case you don't know what an <ID0> or <ID1> is, they're folders named with 32 character, system-specific identifiers. You won't find any folders actually named <ID0> or <ID1>