"Open Project" button will only be enabled when there is a project selected in the active view. If you just downloaded Eclipse and started on a brand new workspace without any project created or imported, you would need to use File > New > Project... or File > Import... to add a project in your workspace.
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…