I called Nintendo today and the speaker was telling me that the Repair men/women told her to tell me to Press and hold the Up on the 4 pointed control stick underneath the C-stick. While holding that also press and hold the A button, L & R button while holding them press the On button and this should activate your 3DS. It should help and i might not help they said so if it does work then your 3DS is fine if it doesn't work then your screwed.
Give it a try! Let me know if it works.