Try this code. You need to declare a method on your code behind that handles the PageIndexChanging event.
protected void grdFiles_PageIndexChanging (object sender, GridViewPageEventArgs e)
{
grdFiles.PageIndex = e.NewPageIndex;
bindGridView()
}
the method bindGridView() is
private void bindGridView()
{
grdFiles.DataSource=.....;
grdFiles.DataBind();
}