Fix PHP Database Connection Error

I have an older php-based website, it is not Wordpress. It is an article directory that is up and running but has lost its capability to post new articles to the database. Also, in its control panel it no longer displays all the categories to post your new article to the proper category (see attached pic). The site became corrupted with these problems after I had someone update it so it could run on a newer php version (required by the host). You can fix these problems either by working with the files and database currently on the site, or install a "virgin" copy of the site I can provide you with, update it to a newer php version that will run, and then plug its current database (about 2,000 articles) into it.

Please respond only if you're sure you have the expertise to fix these problems, do not waste my time and yours.