I have a dropdownlist in my web page and two command buttons and a tabcontainer. The tabcontainer does not appear after the load of page according to my code.

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load     
    If Not IsPostBack Then           
        TabContainer1.Visible = False          
        If CtvAct.GetRecords("Fill_RequestTypeTb") = True Then             
            ReqTypeCmbo.DataSource = CtvAct.MainDataset.Tables("tbOLRequestType").DefaultView             
            ReqTypeCmbo.DataTextField = "RequestTypeName"             
            ReqTypeCmbo.DataValueField = "RequestTypeId"             
            ReqTypeCmbo.DataBind()             
            Dim itm As New ListItem             
            itm.Text = "-- ??? ??? ????? --"             
            itm.Value = "-1"             
            itm.Selected = True             
            ReqTypeCmbo.Items.Insert(0, itm)             
            ReqTypeCmbo.SelectedIndex = 0         
        End If     
    End If 
End Sub   
Protected Sub PrntCmd_Click(ByVal sender As Object, ByVal e As EventArgs) Handles PrntCmd.Click     
    TextBox6.Text = "gggg" 
End Sub

If I press any button after page load the button work very selecting any item from dropdownlist make the tabcontainer appear but after the tabcontainer appear, the buttons does not work (postback) how can I solve these problems