I have the same issue as OP, on my N3DSXL, and this is the only thread I can find on the subject.
I followed these steps:
Steps 1-5
6. Updating B9S
Until I reached this step, where the B9S installer freezes at "FIRM backup hold b to cancel"
If I turn off, I get the blue fading light.
I'm not sure what to do next!
Its been a long time since I first did all this, and I have no idea how it broke after about a year of being on standby.