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It appears most of the database is 'complete'. I can get to all of the "normal" screens (user.php, edituser.php, newbb forum, etc). It appears they may have either replaced your index.php file (or perhaps deleted it) or replaced the contents of mainfile.php.
I'd check the file date/times of index.php, index.html, and mainfile.php as likely suspects with a ftp client. I'd just copy over the index.html and index.php file with those from the XOOPS distribution just to make sure.
You'll need to look at the contents of mainfile.php to make sure it looks 'reasonable' - you can't just copy over it unless you have a previous backup.
In addition to bender's recommendation I would do the following:
1) empty your /cache and /templates directories.
2) put an index.html file in the /cache and /templates_c directories. Use the ones from the 2.0.14 zip file.
3) make sure that mainfile.php is read only (CHMOD 444).
4) delete the /install and /upgrade directories if they exist
