Password Change on SharePoint Machine

Last week my VirtualBox test machine gave me the message "please change your password NOWWWWW", due to (default) Windows 2008 Policy I HAD (no way around this in the login screen) to change the password, so I changed the password....

This is the part where the *** hits the fan... Of course, I installed this demo / test environment easy (quick n dirty) under the Administrator account... That password just got changed so of course SharePoint now gives "Service Unavailable" on every web-application... (including Central Admin)

This problem arises when an account password gets change that is being used by SharePoint as a (managed) account to run SharePoint on.

This is because the Application Pool user that is being used by IIS to host the web-applications no longer has access to the appropriate files and folders, resulting in IIS failure.

Solutions
You can manually change accounts for all application pool users:
- IIS -> application pools->[right mouse on application pool]->advanced settings ->[select the application pool user under “identity” ->click the … and re-fill in all the data of the appropriate user.
This is only HALF the part !
The web-applications will work again now. The only problem is that SharePoint is still “disconnected” from the changed AD-User. You need to update SharePoint with this change.
For instance, creating a new web-application (running under this user-account) will fail because of this mis-sync.

How to fix this ?
Start the SharePoint PowerShell and run the following command: Set-SPManagedAccount –UseExistingPassword
You’ll be prompted to enter the user account & CURRENT (new) password. After a while this command finishes updating the whole of SharePoint and everything is fixed now !

Additional (Technet) information:
http://technet.microsoft.com/en-us/library/ff724280.aspx