TFS Server Troubleshooting

I have a Team Foundation Server (2008) that is currently experiencing issues.? When I attempt to connect to TFS, I receive a 503 Service Unavailable error.? Also, there are errors in the event log: "Login failed for user 'NT AUTHORITY\NETWORK SERVICE'. Reason: Failed to open the explicitly specified database" "The worker process failed to initialize the [login to view URL] communication or the w3svc communication layer and therefore could not be started." "A fatal error occurred during a full-text population and caused the population to be cancelled. Population type is: FULL; database name is TfsWorkItemTracking (id: 14); catalog name is TeamFoundationServer10FullTextCatalog (id: 5); table name WorkItemLongTexts (id: 78623323). Fix the errors that are logged in the full-text crawl log. " "Application pool 'DefaultAppPool' is being automatically disabled due to a series of failures in the process(es) serving that application pool." I need someone who is an expert with SQL Server 2008 and Team Foundation Server 2008 who can quickly troubleshoot and? resolve this issue. I also have a server that we could install TFS 2010 on if it is possible to restore my databases to a new server.