为什么ThreadStart里面的方法不执行解决办法

为什么ThreadStart里面的方法不执行

C# code

private Thread th = null;private Thread thf = null;private void button2_MouseDown(object sender,MouseEventArgs e){ if(checkBox1.Checked) {    thf = new Thread(new ThreadStart(file_transfer));  //file_transfer不执行 } else    m_PCNet.Set(3523,88);  th = new Thread(new ThreadStart(step_for)); //step_for不执行  th.Start();}