//首先导入命名空间

using System.Runtime.InteropServices;

//声明API函数

[DllImport("user32.dll")]
private static extern void LockWorkStation();

//在方法中调用

LockWorkStation();

主要代码片段

[DllImport("user32.dll")]
private static extern void LockWorkStation();
private void btnLock_Click(object sender, EventArgs e)
{
    LockWorkStation();
}