Tap the power button. If the Switch is off, it should turn on. No need to hold it for any length of time.
No luck.
If it doesn't turn on then hold the power button for 12 seconds or longer. If it was somehow frozen then this should hard power it down. Try to turn it on again.
Saw this many times on the net, sadly does not work. Also in a dark room no light comes to the screen at all.
If you still have no joy then connect the Switch to the charger that came with it. (Connect it directly to the Switch, not via the dock)
Tired that and let it charge for 4 hours, sadly nothing .
If that doesn't work then call Nintendo. Something must be wrong hardware wise. If what you said you did was accurate then you haven't done anything that could brick the Switch.
Did that, I finally figure out how to trick the auto help in giving me a number. She red some basic stuff from a script and idiot would already have tried and she issued me a return. I read on line people doing this and Nintendo didnt discover the hack. If they replace the unit ill happily pay for a new license from xecuter.
Honestly, I have had battery issues from day one, I think something was up. Going to let it charge over night but I'm pretty sure its gone. I just didn't know how a switch should act so I thought it was normal.
Thx for the help, long sad day for my and my son.