private void txbPass_KeyPress(object sender, KeyPressEventArgs e)
 {
     Validar.letynum(e);
     if (e.KeyChar == Convert.ToChar(Keys.Enter))
     {
         btnEntrar.PerformClick();
     }
 }
 private void txbUser_KeyPress(object sender, KeyPressEventArgs e)
 {
     Validar.letynum(e);
 }