Run Multiple Threads in Parallel

Hello Experts,

 I'm using the following code to run a Thread in parallel to the program:

            Thread myThread = new System.Threading.Thread(delegate()
            {
                //Your code here
                System.Threading.Thread.Sleep(14000);
                close_window_by_handle(ie);
            });
            myThread.Start();

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In this code I need to wait 14 seconds ( according to the customer request )

the problem is when I run this code few times during 14 seconds it stuck

 How do I enhance my code check if a thread is running, if YES it create a new thread in addition to the running  one
else it use the Stopped thread

Thanks