I had to migrate a MOSS 2007 farm to SharePoint 2010. – After migration the SharePoint Help did not work. (It’s the button upper right on a SharePoint site.)
A popup window appeared and I got an empty site with the message “Help not available” (or something like that: It was a german site so the error message was german…)
I tried a new created web application with a Team Site collection. There the help does work as expected.
Then I had a look into the Windows Event Log. There I found a related error. The web application pool account of my migrated web application did not has access to the Admin Content database. But the application pool account of the new created web application was enabled to access this database. – After adding the application pool account of my migrated web application as “db_owner” the help was shown as expected.
(I have no screenshots of that. Sorry. But I think, that can be reproduced easily by removing the application pool account from the Admin Content database.)