SharePoint site shows 'Service Unavailable. HTTP Error 503. The service is unavailable'

一段时间没开SharePoint server，一启动发现Central Administration不能访问了，显示Service Unavailable HTTP Error 503. The service is unavailable, 如下图：

解决方法：

1. Go to Start >> All Programs >> Administrative Tools >> Internet Information Services (IIS) Manager.
2. Locate your App Pool account(such as SharePoint Central Administration v4, the third line on right panel, see below figure) and right-click on it and select ‘Advanced Settings’.
3. Go to process model then Identity Click on the Identity >> Set and then give the user name, password and confirm password.

原因可能是账户密码过期了，需要重置一下。

参考：
https://sharepoint.stackexchange.com/questions/22605/http-503-service-unavailable-error-messages-when-attempting-to-open-sharepoint