createFile

if (File.Exists(@"E:\Prosits\22 - Services Windows\Test\fichier4.txt"))
{
    StreamWriter sw = new StreamWriter(@"E:\Prosits\22 - Services Windows\Test\fichier5.txt");
    sw.WriteLine(DateTime.Now.ToString());
    sw.Close();
}
else
{
    TextWriter file = File.CreateText(@"E:\Prosits\22 - Services Windows\Test\fichier5.txt");
    file.WriteLine(DateTime.Now.ToString());
    file.Close();
}