Any Luck Mate ? im actually not much help im more curious to the situation of yours ....... i think its simply either the SD Card ... maybe not formatted properly or you did not follow the guide PERFECTLY ........... maybe unlikely ... for my sons n3ds i had a similar issue ... after doing a long ass hack ( only long because i struggled by rushing things ...) everything was fine ect working .... and then we found Moflex movies in 3D for n3ds so i had to keep taking out SD Card ..>> Back in Pc ect ..Changing his films .....Long Story Short ... the SD Card would not read 3DS was not staying on a bit like yours .... all i did was simply was i put some sellotape around the to of the SD Card .. then it held hard in the back of the 3DS .. & everything has been fine since .... & i did this last summer time.... hope you figure this out