A missing file from the ctrnand could result in a black screen (i’ve had that happen myself). Go to 3ds.hacks.guide and follow their region changing tutorial (if there is a file missing, this should fix that)
Video guides are often inaccurate and outdated. Try using safe mode to update the system. (this can be done by holding down L + R + D-Pad Up + A, and then powering on the system.