Alright, that was helpful. So what's happening in this video is that when you power in on with the SD card inserted, you briefly see the Luma3DS config screen (because SD:/luma/config.bin is either missing or old) then it powers off. When you take the SD card out, it tries to boot from Luma3DS on the NAND, which does have a config file and so it doesn't show the config screen and attempts to boot, but gets stuck on a black screen (something is bad in your NAND). Lastly, if you put the SD card in and hold Start while booting, it tries to load whatever is in your payloads folder, can't, and powers off.
Why the 3DS powers off when trying to show the config file, I'm not sure. Do you have this file: SD:/luma/config.bin? If so, try deleting it. Power your 3DS on normally without holding any buttons and see if the config screen comes up and stays up or if it powers off again.