You might want to check inside the usb connector to make sure none of the pins are bent or touching one another.

Try pressing F2 on bootup and then go into set and turn SecureBook off. That should let it boot up fully.

I too had this same issue after my son had jammed his SD card into the slot backwards. When this happens it bends the switch for the SD card write protect in the slot. Its not the card that is the issue but the slot itself. If you look into the sd slot you will see this switch. It looks like a tiny half paper clip shape. It is on the right side of the slot when the 2DS is laying on its back. All I did to fix it was reach in with a very fine 1mm flat head screwdriver and bend the switch up a little bit. The switch was bent down so the card was always reading as write protected. After I bent it up, the switch would fit into the proper gap on the card when the switch was not in write protect mode and therefore the 2DS would see the card as not being write protected. This fixed the issue on my 2DS.