use of lock object

[atuvy]

I am writing a dll which runs several threads reading from a Queue, the calling program calls EnqueueTask with a data object. If I use lock around the queue object nothing goes in the queue, if I comment the lock than it works well (but causes a problem with the threads)
Please help

public class messagesQueue :IDisposable
    {
        EventWaitHandle waitHandle = new AutoResetEvent (false);
        Thread _workerThread;
        object locker = new object();
        Queue<reportData> _messageQueue;// = new Queue<reportData>();
        
        
        /// <summary>
        /// Constructor
        /// </summary>
        public messagesQueue()
        {
            _messageQueue = new Queue<reportData>();
        }
        /// <summary>
        /// Add record to the queue
        /// </summary>
        /// <param name="reportDataObj"></param>
        public void EnqueueTask(reportData reportDataObj)
        {
            lock (locker)
            {
                _messageQueue.Enqueue(reportDataObj);
            }
            waitHandle.Set();
        }