My 3DS wouldn’t power on this morning. I hadn’t used it for a week. I guess the battery was as flat as a pancake. After charging the 3DS for an hour it still wouldn’t power on (it was still plugged into the mains and charging as far as I could tell).
Hmm. That’s a bit weird I thought. In a fit of desperation/pique I removed the game card (Mario Kart 7) and I removed the SD Card too. I immediately tried to power on the 3DS and bingo it came on first time. I powered it down again, put the SD card and game card back in and bingo, it powered up again.