Re: Serious Server Issues…
I am fairly certain the bb-admin/install.php checks for a previous installation. So, download the new files, copy config-sample.php over to config.php and run bb-admin/install.php. If it notices you’ve already installed, it should give you a warning that it’s already installed, and that maybe you meant to run the upgrade script. The upgrade is only useful for old installations, I think, so ignore that.
The other option is that you would just download the files and put them in the same place (replacing everything you deleted). Edit the config.php (copy config-sample.php over to config.php and edit that) and try browsing the forum. Do not run the installer. If the database tables are still there, I think this will work.
Hopefully the version you installed is still available for download (was yours 0.75?)
Of course, this is all just a guess. Can’t hurt to try though.