Just hold the power for +20 seconds, which should turn your switch off.
Leave your Switch chaging for an hour with a charger.
It also won't boot if the battery is empty.
Use lockpick_rcm as a payload to see if you can inject something properly.
If that works, make sure you have put all the Atmosphere files in the right folders on your SD card (preferably FAT32).
Then inject the primary payload.
If the SD card is messed up or the required files are missing, you'll also get a black screen.
And if you managed to get everythign working again, please share it here so that people can use it as a reference in case they have the same issue.
Thanks!