Application Pool is auto stopped when browse web application in IIS6

I am unable to view the page. I get the following error: Service Unavailable

HTTP Error 503. The service is unavailable.

The Application Pool of IIS 6 is shown as stopped. All web applications have this problem.

1.      Go to IIS -> Application Pool

2.      Under the Advanced Settings à click on identity under Process Model

3.      Go to Built-in account à Choose NetworkService

Navigation: Process Model TabàIdentityàNetworkService

After Change Showing just like this.

Restart the application pool and check.