Q:

C# Windows Service that has no work to do

I have created a C# windows service that should send some emails but when I start the service I receive the message 'the service on the local started and then stopped'... 'some services stop automatically if they have no work to do'
Why would this be?
namespace EmailService
{
public partial class EmailService : ServiceBase
{
    private System.Timers.Timer _timer = null;
    private DateTime _lastRun = DateTime.Now;
    private int _timerIntervalValue;

    public EmailService()
    {
        InitializeComponent();
    }

    protected override void OnStart(string[] args)
    {

        if (string.IsNullOrEmpty(ConfigurationManager.AppSettings["Timer"]))
        {
            throw new Exception("The timer value is not set in the app.config.");
        }
        else
        {
            _timerIntervalValue = Convert.ToInt32(ConfigurationManager.AppSettings["Timer"]);
        }

        _timer = new System.Timers.Timer(_timerIntervalValue);
        _timer.Elapsed += OnTimedEvent;
        _timer.Interval = Convert.ToInt32(_timerIntervalValue);
        _timer.Enabled = true;

    }

    protected override void OnStop()
    {
        _timer.Stop();
        _timer.Dispose();
    }

    private void OnTimedEvent(object source, ElapsedEventArgs e)
    {
        Email email = new Email();
        email.ProcessEmails();
        _lastRun = DateTime.Now;
        _timer.Start();
    }

}

}

Event Log entry
Service cannot be started. System.Security.SecurityException: The source was not found, but some or all event logs could not be searched.  Inaccessible logs: Security.
   at System.Diagnostics.EventLog.FindSourceRegistration(String source, String machineName, Boolean readOnly)
   at System.Diagnostics.EventLog.SourceExists(String source, String machineName)
   at System.Diagnostics.EventLog.SourceExists(String source)

A:

You need to start a Foreground thread to keep process from exiting.  
This is only achieved by creating new Thread. A Timer works as a background thread. See update below!
See my answer here:
Best use of Windows Service for repeating a program call

This is a VERY SIMPLISTIC approach:
public partial class EmailService : ServiceBase
{
    Thread _thread = new Thread(DoAlways)

     protected override void OnStart(string[] args)
     {
        _thread.Start();
     }

     private void DoAlways()
     {
        while()
        {
           // ...
        }
     }

UPDATE
Timer of a type System.Timers.Timer uses System.Threading.Timer which in turn uses a native WIN32 timer.
I did compile and install your service on my machine (XP) and it just worked.  Service started with no problem.I suggest that you hard-code the interval value to see if it works since I suspect it gets a value of zero hence timer never initialised.

