can;t download the file from webmethod

i taired a lot of to download a file using webmethod.my ajax function is ok but when i click my download button it shows no result.
//this is my c# code... [System.Web.Services.WebMethod()] public static string downloadfile(string path) { try { string str = HttpContext.Current.Server.MapPath("~/Files") + "\\" + (HttpContext.Current.Session["ProjectId"]) + "\\" + path; // Create New instance of FileInfo class to get the properties of the file being downloaded FileInfo myfile = new FileInfo(str); // Checking if file exists if (myfile.Exists) { //System.Web.HttpResponse Response = System.Web.HttpContext.Current.Response; // Clear the content of the response HttpContext.Current.Response.ClearContent(); // Add the fil ...