Error log to look for would be the Apache error log and/or the PHP error log (if this is separate on your server). I can't tell you where to look for the log on your server, because the location depends on the server setup. Maybe your support can tell you where to find it if you can't locate it on your own.
If the error occurs immediatelly after entering the database details, there might be a problem connecting with the database. It could be that the database is not correctly created (re-created) or you might have entered something wrong resulting in Elgg can't connect with the database.
You can check if elgg-config/settings.php already exists (it gets created during the installation). If it's already there, you can check if the database connection details are correct (and fix it if not). Or you could delete the settings.php file and re-start the installation.
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