When I edit the code ar add my own edits, I simply use Wordpad..
You can try moving your existing config.php file to a different location temporarily, deleting your old forum directory and uploading a fresh copy of version 2.0.16 from the phpBB site. Delete the new config.php file as well as the install and contrib directories and move the originalconfig.php file back into the root folder and see if that fixes your problems.
If you don't have any MODS installed this would probably be the easiest and quickest route to go.