Static method does not recognize fields in aspx

Question

This method needs to be Static

[WebMethod]
        public void ValidaSenhaAntiga(object sender, EventArgs e)
        {
            long CPF = Helper.DFrmtCPF(cpf.Value);
            string senhaAtual = SenhaAtual.Value;
            bool senhaAt = ws_usuario.getSenhaAtual(senhaAtual);
            if (!senhaAt)
                lblMsg1.Text = Helper.ExibirMsgAlerta("A senha não confere.");
        }

The problem is that when I put Static it does not recognize SenhaAtual.Value and neither cpf.Value, because these fields come from a page aspx. I am using the PageMethods and from the research I’ve done on the Internet it only works with public static. What I am doing is for javascript to execute a method in the code Behind, to validate a password, that is, in the Passwords field the user enters the current password and this function searches in the BD and compares with what the user typed and returns true or false. How do I use the PageMethods, methodically public static and fields of aspx? No js have it, but I need to get better:

function ValidaSenhaAtual() {
    PageMethods.ValidaSenhaAntiga(true, false);
}

This edition, I tried to do otherwise. I created this js function

function ValidaSenhaAtual() {
    $.get('minha_pagina.aspx/ValidaSenhaAntiga', {
        NovaSenha: $('#conteudo_SenhaAtual').val()
    }, function (data) {
        if (data.senhaAt === true)
            alert('ok');
    });
}  

To call this method in code Behind

[WebMethod]
        public void ValidaSenhaAntiga(string NovaSenha)
        {
            //long CPF = Helper.DFrmtCPF(cpf.Value);
            //string senhaAtual = SenhaAtual.Value;
            bool senhaAt = ws_usuario.getSenhaAtual(NovaSenha);
            //if (!senhaAt)
               // lblMsg1.Text = Helper.ExibirMsgAlerta("A senha não confere.");
        } 

This approach doesn’t work either. I think this $.get('minha_pagina.aspx/ValidaSenhaAntiga is wrong. When you reach this line, it skips the function.