My 3ds is off when I turn it on the blue Led turns on for half a second then turns off. Nothing else happens the screen stays off.

I think the problem is that it reads my CTR NAND boot.firm and not the one from my sd cardDownload Luma 7.1 and put the boot.firm (overwriting any that is already there) on your SD card. If that doesn't work, try Luma 8.0. One of them should work.

Then try with another SD card --- the SD should take priority. If it doesn't, that's a big bug.I think the problem is that it reads my CTR NAND boot.firm and not the one from my sd card