Troubleshooting log: web application unavailable

I was asked to server room late night last Friday because any access
to any web application got only an error of "Server Application
Unavailable". At the very beginning a power cord to the database
server disfunctioned so they powered that server off and replaced the
old cord with a new one then restart the database server but found
only a few web applications were available while some others could not
be accessed. They chose to restart IIS, however, boom, now none of the
applications were available but a "Server Application Unavailable "
error message.

I opened event view window and went to the first error of that day, it says,
aspnet_wp.exe could not be launched because the username and/or
password supplied in the processModel section of the config file are
invalid.
and,
aspnet_wp.exe could not be started. The error code for the failure
is 80004005. This error can be caused when the worker process account
has insufficient rights to read the .NET Framework files. Please
ensure that the .NET Framework is correctly installed and that the
ACLs on the installation directory allow access to the configured
account.

I know only Windows itself controls the password of ASP.Net so how
could the password be wrong. Open account information of this user,
my, it was locked out. Enable it again and all the applications went
back to work.