I had the same problem...
What problem was that? You can log in as the Administrator and from the Admin menu, select Event Viewer to see all the errors.
The:
"'/App_Code/ADefHelpDesk/dnnHelpDeskDAL.designer.cs' use a different language, which is not allowed since they need to be compiled together" error
is because the installation directions were not followed and Linqprep was not installed or Asp.net 3.5 and SQL 2005 or higher was not installed.