See This

Add following code to click event of login button

and pass the parameters username and password like this.

GetDataSet is the function for getting values in dataset from your database.

        str = "SP_LOGIN '" & txtUsername.Text & "','" & txtPassword.Text & "'"
        ds = obj.GetDataSet(str)
        If ds.Tables(0).Rows.Count > 0 Then           
                Response.Redirect("Details.aspx")
        Else
                lblError.Visible = True
        End If