Have you photos about your system, power connected and so on.
"Using the support, the PCB must be floated in the air to turn on." This could mean a short circuit below your board, or your board is broken and needs to lifted just right to work. But this is all quess work, without seeing the board.
Remove all power wires and so on, so that there is no power on your board, then measure all ground points with ohm meter if they are connected together. Hold the board good and bad positions. You should see some difference.
Then repeat the same with +5V.
What material is your table made of. Metal is bad here.
One more thing. What kind of power supply you have. Is it possible that it has too much noise for your board to work. Or reset does not work. Try holding the reset pin down a moment, does your board start then.