You can use the following function in a Web Service or any other types of 
project.
Juz pass a URL to the function and it will return true if the URL is valid.

    ' This function checks whether a file exists on a remote server.
    ' It will return True if that file exists, and False if it doesn't.
    '
    ' Depending on the Web Server which is hosting your file,
    ' the url to your file may/maynot be case-sensitive
    ' e.g. the following url will return True
    ' http://sg.geocities.com/mangokun/images/settings.ico
    ' HttP://sG.geOcities.com/mAngokun/images/settings.ico
    ' but the rest below will return False
    ' http://sg.geocities.com/mangokun/imageS/settings.ico
    ' http://sg.geocities.com/mangokun/images/Settings.ico
    ' therefore in my case, sub-dirs and files must follow what I named 
them in my web dir.

    <WebMethod()> Public Function IfWReqFileExist(ByVal strUri As String) 
As Boolean
        Try
            Dim WReq As WebRequest = WebRequest.Create(strUri)
            Dim WResp As WebResponse = WReq.GetResponse()
            WResp.Close()
            Return True
        Catch
            Return False
        End Try
    End Function

    ' If you like, you can use this instead of the one above
    <WebMethod()> Public Function IfHttpWReqFileExist(ByVal strHttpUri As 
String) As Boolean
        Try
            Dim HttpWReq As HttpWebRequest = CType(WebRequest.Create
(strHttpUri), HttpWebRequest)
            ' Turn off connection keep-alives.
            HttpWReq.KeepAlive = False
            Dim HttpWResp As HttpWebResponse = CType(HttpWReq.GetResponse
(), HttpWebResponse)
            HttpWResp.Close()
            Return True
        Catch
            Return False
        End Try
    End Function



Previous message:
> I used to have a link-checker script that would go through a table of 
URLs in a database and issue a request/response to check their server 
status code and description, and report this info back to me. It wasn't 
very scalable, and I am trying to re-write in ASP.NET.After some testing, 
I am confused as to how to do this with ASP.NET. It would seem that the 
HttpWebRequest and HttpWebResponse classes in the System.Net namespace 
should do the trick, as the latter has StatusCode and StatusDescription 
properties.But when I try the code below with test URLs, I don't get the 
desired results. If I try a known URL, like my own 
http://www.epistemelinks.com/, then I get back a statuscode of OK as I 
should. If I try one that should return 404 error, I still get OK. If I 
try one that doesn't even resolve as a domain name, then one of the 
exceptions fires instead (which is fine).I am using the wrong classes for 
what I am trying to do? How can I write some simple code to properly check 
for 200 = OK vs. 404 = Page Not Found vs. 500 = Error and so forth?
Thanks,Tom S.  private void Page_Load(object sender, System.EventArgs e){  
try  {    HttpWebRequest objHttpWebRequest = (HttpWebRequest)
WebRequest.Create("http://www.epistemelinks.com/nopagehere.aspx");     
HttpWebResponse objHttpWebResponse = (HttpWebResponse)
objHttpWebRequest.GetResponse();     string strData = 
objHttpWebResponse.StatusCode.ToString() + " ";    strData += 
objHttpWebResponse.StatusDescription + " ";    strData += 
objHttpWebResponse.LastModified.ToString();    objHttpWebResponse.Close
();    Heading.InnerHtml = "ELC Link Checker Tool";    Intro.InnerHtml 
= "Your query returned the following report:";    SearchResults.InnerHtml 
= strData;}  catch(WebException ex)   {    SearchResults.InnerHtml 
= "WebException raised: " + ex.Status;   }  catch(Exception ex)  {    
SearchResults.InnerHtml = "xception raised: " + ex.Message;  }}