Also try to boot it without the sd card and gateway3ds inserted, The safe boot method IIRC will update your 3ds to latest version (or is that the recovery mode?).
Bricked then u need a nand mod. Send your 3ds to someone in your country that's trusted on this forum. if you do that you can restore your nand backup.
I hope someone just butt-fucks gateway by hacking their launcher.dat and making it boot into "gateway" mode but with devmenu already installed. Then we can watch as they fall and die out.
Exact same thing for me, It seems to crash on windows 8.1 not sure for windows 8. For a workaround IF you can, you can download virtual box and download a windows 7 iso and run it and it should work from there.