1. I recommend finding a text editor that will show you line numbers. If you’re using Windows, a decent open source editors is Syn Text Editor. If you’re using some distro of linux; I like using Bluefish. If you’re using a Mac, I’ve heard good things about BBEdit; but I don’t have a Mac and can’t make any real recommendations.
2. The error message tells us that something is wrong with your index.php file around that line 58 but without seeing the code in your index.php; we can’t really say what’s wrong. I’d recommend you copy all of the code from your index.php in a text file (txt) and post that on your site so that people can see your code and possibly make suggestions to help you out.