Error while writing to event log, prevents windows service from starting?

I am using the following code to create a custom event log in my windows service application:

public ServiceConstructor()
{
  InitializeComponent();
  if (!EventLog.SourceExists("WinService"))
  {
    EventLog.CreateEventSource("WinService", "WinServiceLog");
    eventLog1.Source = "WinService";
    eventLog1.Log = "WinServiceLog";
  }
}
protected override void OnStart(string[] args)
{
 eventLog1.WriteEntry("Started");
}

After installing the service.msi, when i started the service it started and then stoped. Then i found the following error in EventViewer windows log section:

Service cannot be started. System.ArgumentException: Source property was not set before writing to the event log.

at System.Diagnostics.EventLog.WriteEntry(String message, EventLogEntryType type, Int32 eventID, Int16 category, Byte[] rawData) at System.Diagnostics.EventLog.WriteEntry(String message) at WinService.Service.OnStart(String[] args) at System.ServiceProcess.ServiceBase.ServiceQueuedMainCallback(Object state)