If your SSRS does not start and worst unable to completely start with the following exception thrown at event viewer
Application: RSHostingService.exe
Framework Version: v4.0.30319
Description: The process was terminated due to an unhandled exception.
Exception Info: System.Xml.XmlException
at System.Xml.XmlTextReaderImpl.Throw(System.Exception)
at System.Xml.XmlTextReaderImpl.ParseRootLevelWhitespace()
at System.Xml.XmlTextReaderImpl.ParseDocumentContent()
at System.Xml.XmlReader.MoveToContent()
at System.Xml.Linq.XElement.Load(System.Xml.XmlReader, System.Xml.Linq.LoadOptions)
at System.Xml.Linq.XElement.Load(System.String, System.Xml.Linq.LoadOptions)
at Microsoft.BIServer.Configuration.ConfigReader..ctor(System.String)
at Microsoft.BIServer.BIService.ServiceConfig..ctor(System.String)
at Microsoft.BIServer.BIService.BIService.SetNewConfigFilePathIfExists(System.String)
at Microsoft.BIServer.BIService.BIService..ctor()
at Microsoft.BIServer.BIService.Program.Main()
Also tried to repair the installation and the process ALWAYS fails.
My solution here was to delete the SSRS folder at the default installation folder of
C:\Program Files\Microsoft SQL Server Reporting Services
After that reinstall the ssrs.
Register the old reportserver database in the report server configuration.
Happy Coding!