as others have said new line char will give you a new line in a text file in windows.
try the following:
using System;
using System.IO;
static class Program
{
    static void Main()
    {
        WriteToFile
        (
        @"C:\test.txt",
        "fkdfdsfdflkdkfk@dfsdfjk72388389@kdkfkdfkkl@jkdjkfjd@jjjk@",
        "@"
        );
        /*
        output in test.txt in windows =
        fkdfdsfdflkdkfk@
        dfsdfjk72388389@
        kdkfkdfkkl@
        jkdjkfjd@
        jjjk@ 
        */
    }
    public static void WriteToFile(string filename, string text, string newLineDelim)
    {
        bool equal = Environment.NewLine == "\r\n";
        //Environment.NewLine == \r\n = True
        Console.WriteLine("Environment.NewLine == \\r\\n = {0}", equal);
        //replace newLineDelim with newLineDelim + a new line
        //trim to get rid of any new lines chars at the end of the file
        string filetext = text.Replace(newLineDelim, newLineDelim + Environment.NewLine).Trim();
        using (StreamWriter sw = new StreamWriter(File.OpenWrite(filename)))
        {
            sw.Write(filetext);
        }
    }
}