I would say the sound of the disconnect/reconnect isn’t a good sign, but touching the black part of the antenna shouldn’t have caused anything. If the board shifted onto something metal (aluminum phone or laptop case or such) that might have connected pins oddly on the back it might have caused a jolt in the power on the USB which can sometimes cause windows to block that USB port until the next restart. It definitely is possible to completely fry a Mayfly but when I’ve done it it’s been doing something a bit more foolish than just putting it on top of something metal. If Windows blocked the USB port due to a surge, you must restart your computer and then it should be unblocked.
I don’t know anything about the Java errors you posted in the first post. That sounds like an error with the Arduino IDE itself not with your code. I’d suggest restarting your computer for that, too.
In the last post where you tried the blink sketch, it said the serial port was not selected and it compiled for the UNO. You need to set the board to “EnviroDIY Mayfly 1284p” by using the “Board” option in the tools menu. You also need to set the port to COM# of whatever Windows assigned it when it first connected. If you did cause a surge on the USB and Windows shut it down, then you won’t see any options possible for the port until you’ve restarted. If you still don’t see anything after restarting and Windows is making the “connected” and “disconnected” sounds when you unplug and re-plug the Mayfly to the USB there might be a problem with your FTDI drivers.