Recently on my Windows 7 developer machine the application pool on my local IIS 7.5 web server stopped working immediately after it was (re)started. In the in the event viewer I found an error (Event ID 5059) that says:
“Application pool […] has been disabled. Windows Process Activation Service (WAS) encountered a failure when it started a worker process to serve the application pool.”
You can find more information about “Event ID 5059 — IIS Application Pool Availability” here.
After some try and error I found out, that the app pool was configured to use my domain account as identity and I remembered that I changed the password of my domain account shorty before. Resetting the application pool’s identity (using my new password) fixed the problem and the app pool could be restarted without any problems.