I do not have the log file to upload as explained below.
My provider's server had a hard disk crash yesterday and restored a server backup from 31st Dec. The website I was working on is an upgrade from Version 3 to version 4 and the restoration was causing problems so I restored a backup from my hard disk. It is set up as a temporary subdomain on another account I have. It was working fine before the hard disk crash.
I only have one backup file (I can supply a download link privately). Unfortunately the log files associated with it were lost during the system restore - there are no logs in the backup folder at all.
The restore appears to work correctly and, as a work in progress, the website appears correctly. However when I try to go to the admin page it automatically redirects to the site homepage again so I can't login as administrator.
I have ADMINTOOLS installed too (link available privately) but it makes no difference if I replace .htaccess with a stock Joomla version
I have enabled debugging and it is showing mail errors
I have no idea what is going on - I have another subdomain j4test.lairdswood.com that restored and works fine both in the front and back ends.