Luckily, its not such a big disaster as the site was yet to be developed, there was nothing in the database yet!What happened:
A virgin installation of Joomla 1.5 was mistakenly loaded onto our brand new site rather than the most recent Joomla 2.5.
Trying to fix it, I upgraded to 2.5. It went smoothly until I tried to move the Joomla folders and files into a new folder in the root: public_html/myoldsite.
I wasnt paying attention and moved the Jupgrade folder as well. I moved it back immediately.
I checked the front end and saw this:
Index of /
Which is ok, but when I try to log into backend Joomla administrator I see this:
The requested URL /administrator was not found on this server.
Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.
Would it be easier to delete and start again with a proper Joomla 2.5 install rather than try to find out how I messed up moving the files?