Fill DataGrid In Connected Mode

I made a web application through VB & ASP .NET contains dropDownList Box &
DataGrid, DataGrid must be filled with Products when I select Any item from
DropDownList Box "Category" - Connected mode , Northwind database.
But When I run the application The DataGrid did't display in the web page, & I'
sure that all my steps are right, but I do't know why the DataGrid did't display
.
Can anyone help me.

As per the behaviour,if datagrid is not displayed if data is not filled in
datagrid . check with our code once again.if data is filled in page_load event
then it wll be displayed.