How to keep web service start and running without manual intervention

A Web Service is programmable application logic accessible via standard Web protocols.
Web services are components on a Web server that a client application can call by making HTTP requests across the Web.

Yes, you need to call the methods programatically from other programs (projects), and also you can schedule those projects. So your web service will get run through schedule task.

You need to be more specific when asking question. Members like me sometimes get confused and will not post a reply. 

If you host the web service as new application/web site, automatically it will whenever the IIS starts. For the newly created website you can set the "Start Automatically" property as "True" (I've checked in windows 7) .




Windows Service

Microsoft Windows services, formerly known as NT services, enable you to create long-running executable applications that run in their own Windows sessions. These services can be automatically started when the computer boots, can be paused and restarted, and do not show any user interface. These features make services ideal for use on a server or whenever you need long-running functionality that does not interfere with other users who are working on the same computer. You can also run services in the security context of a specific user account that is different from the logged-on user or the default computer account.

http://msdn.microsoft.com/en-us/library/d56de412%28v=vs.80%29.aspx
http://www.codeproject.com/KB/dotnet/simplewindowsservice.aspx

Hope this helps you.