Hi,
You can check particular web service is exists or not by using my code
WebRequest req = WebRequest.Create("http://www.webservicex.net/ConvertAcceleration.asmx");
try
{
WebResponse res = req.GetResponse();
}
catch (Exception es)
{
}
If you give wrong webservice url it just raise Exception.In that catch method you can write user friendsly msg
And you can use dispose method to disable webservice .Am not sure about this
but you can try that .
You can disable and enable webservice which is in your local website.
Here I'm providing some links to understand more about webservices.
http://msdn.microsoft.com/en-us/library/ms972326.aspx
All the Best