SharePoint: Service unavailable

If you receive "Service unavailable" then you try to open SharePoint 2007 Central Administration then it means your application pool for it (usually "SharePoint Central Administration v3") is stopped. But if you start it and it stops again, as you try to open administration page, then it means that you farm credentials are corrupted. This worked for me as a fix:

stsadm -o updatefarmcredentials -userlogin DOMAIN\login -password password

then run:

iisreset /noforce

and have a nice day.