"The identity of application pool SBS Sharepoint AppPool is invalid"

We have SBS2011.  After a recent server reboot the Companyweb Sharepoint site was not working (HTTP Error 503: The service is unavailable.) and I noticed that services running as DOMAIN\spfarm had not started with a logon error, i.e.:

SharePoint 2010 Timer
SharePoint 2010 VSS Writer

So I changed the AD password for that account and updated the services - they now start.  However, no change with the Sharepoint site, and the following errors in the System log, all from source WAS:

5021: The identity of application pool SharePoint Central Administration v4 is invalid.
5057: Application pool SharePoint Central Administration v4 has been disabled.
5059: Application pool SharePoint Central Administration v4 has been disabled.

Plus the same three errors for the "SBS Sharepoint AppPool".

I checked the membership of DOMAIN\spfarm, it is a member of IIS_IUSRS and IIS_WPG, as is DOMAIN\sbswebapp.  Both groups have "Logon as a batch job" set in the Default Domain Controllers Group Policy.

I was able to fix the SharePoint Central Administration v4 errors by running the following command:

STSADM -o updatefarmcredentials -userlogin DOMAIN\spfarm -password [AD password]

So now I can run Central Administration, but still not the Sharepoint site.

What steps must I take next?

David HaycoxConsultant EngineerAsked:
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David HaycoxConsultant EngineerAuthor Commented:
Fixed it by changing the credentials in:

IIS Manager
Application Pools
SBS Sharepoint Application Pool
Advanced Settings
Process Model

Still a mystery as to why it suddenly stopped working though.

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