Q: I'm unable to select a particular chess piece on the board and I want to move it, why?

A: If you are unable to select a particular chess piece on the board, that means it has no valid moves available. Most often it happens when the piece is "pinned" -- i.e. it is in the way of an attacking piece of the opposite color, so you cannot move your piece without placing your King in check. In other words, the chess piece you are trying to move is protecting your King from being captured, so it cannot be moved.