Binding gridview with where clause does not work

I have a gridview filled with product information. SQL table looks like this:
ID||UserID||Name||Price||
and I want that the ID of the product matches with the id of the Users (User_ID). (I have a own SQL table with User Information).
I have this Code, but the gridview does not show something. Its just empty...

protected void BindGrid()

        { string constr = ConfigurationManager.ConnectionStrings["strConn"].ConnectionString;
            using (SqlConnection conn = new SqlConnection(constr))
            {

                using (SqlCommand cmd = new SqlCommand())
                { //Land ergänzen
                    cmd.Connection = conn;
                    cmd.CommandText = "SELECT * From Product WHERE UserID=@UserID";
                    cmd.Parameters.Add("@UserID", SessionHelper.User.ID);
                    using (SqlDataAdapter ad = new SqlDataAdapter(cmd))
                    {
                        DataTable dt = new DataTable();
                        ad.Fill(dt);
                        GridView1.DataSource = dt;
                        GridView1.DataBind();
                    }
                }
            }
        }