Yeah - tried that about two days ago, with no changes.
I think I’m just gonna accept that my console is a lost cause, and hit up one of the retro game stores near where I live to nab a new one down the line.
First, try re-downloading the Luma3DS and DO_NOT_LAUNCH.firm from the guide and follow the instructions regarding them. Ensure that the option to show file extensions is enabled, and make sure the "boot.firm" is placed on the root of the SD Card, and that it has that exact name. If, after following tnose instructions, your 3DS still does not boot, then try holding down START before and during boot, and see if you can get into GodMode9. If you can, then copy the "boot.firm" from the SD Card (0:/) to the CTRNAND (1:/) and then copy the "luma" folder from the SD Card (0:/) to the CTRNAND's "rw" folder (1:/rw). When you do these, GodMode9 may issue a dire warning, if it does, then ignore it and press the key sequence to unlock the write permission for both operations. If it still doesn't work, then copy the "boot.firm" and "luma" from the SD Card to different SD Cards. Try as many SD Cards as possible.
If it still doesn't work, then one of these two things is happening:
1: Your 3DS's SD Card reader ramdomly broke as soon as you ran the B9S installer...
or:
2. You're lying.