I have started a SharePoint server which was down for last 4 months. Now, the problem is that whenever I am trying to open SharePoint Central Administration, Service Unavailable: HTTP Error 503 is displayed. On investigating the problem, I saw that the App Pool is not running. And now, no matter whatever I try, its not starting. Any suggestions?
In this case there are multiple reasons for this issue, you have to check the Event Log ( security & Application) and you will get the reason.
You said farm was shut off for 4 months than most probably your password expired. You have to change the password for the central admin app pool from IIS itself. After that you have to update the password inside SharePoint for Timer service etc.
- I would try the below stsadm command, mostly probably that account will be your farm admin account thats mean everything not working ( you can check under which account sharepoint timer service is running, if it is same account as central admin app pool), try this
stsadm –o updatefarmcredentials –userlogin DOMAIN\username –password $password$
another reason could be related to permission.