Service unavailable identicate that .NetFramework is failing in the IIS, verify this
Go to IIS > Websites > properties > ISAPI filter ::: You will see aspnet 2.0 filter if it is showing in RED down Arrow. Then Remove it and restart IIS
Check if HC website is running under aspnet 2.0 version
Go to IIS > Websites > Hosting Controller > Properties > aspnet tab ::: Make sure .net 2.0 version is enable.
If above suggestions didn't help, then follow this
Open command prompt select path
Hopefully this will helps to resolve the issue.