Hi Dave,
The problem you have is common on some servers. It all boils down to how you install Moodle. If you used a FTP client like File Zilla rather than your host companies control panel (cPanel), then this is where the problem stems from.
What has happend is that some of the PHP files have been corrupted, overwritten, or rather stripped of the formatting, and therefore rendered useless by your server.
The best way to fix this is start over again, but be sure to use the cPamel to upload the zip file and then extract it into your Moodle directory.
However before you do this check your root config.php and also the standard theme's config.php, it may just be more likely that these have been corrupted.
I hope this helps?
Mary