ASP.NET

function ValidatePage()
{
  return Page_Validate("VALIDATION GROUP NAME");
}

<asp:CustomValidator ID="CustomValidator1" runat="server" 
                                      ClientValidationFunction="CheckPorts" ControlToValidate="txtPort" 
                                      ErrorMessage="Please checked at checkbox or enter Port code in textbox." ValidateEmptyText="True"  
                                      ValidationGroup="RegisterAgentUser">*</asp:CustomValidator>

function CheckPorts(sender, args) {
        var chk = document.getElementById('<%= CType(CreateUserWizardStep1.ContentTemplateContainer.FindControl("chkViewAll"), CheckBox).ClientID %>')
        if (args.Value == "" && chk.checked == false) {
            args.IsValid = false;
             }
        else {
            args.IsValid = true;
        }
    }

IRequiresSessionState

public class Handler : IHttpHandler,IRequiresSessionState 
{
...

<div id="progress" style="visibility:hidden">Please wait...</div>

<input type="button" onclick="showProgress()"/>

function showProgress()
{
 $("#progress").show();
}

buffering83 wrote:

If you know site which explain simeple way.

If Not IsPostBack Then
	'BindCombobox here
End If