>I am about to reformat C: drive where SQL Server 2008 is installed but not working. Any files (besides databases) I need to copy to external drive so that when I install the SQL Server again, I can use these configuration files?
>TIA

Something you can do is go to the folder where you installed SQL Server (the one that is not working) and navigate to "Setup Boostrap\Log\(latest installation)" (for example in my computer C:\Program Files\Microsoft SQL Server\120\Setup Bootstrap\Log\20140728_112603) find the file ConfigurationFile.ini and copy it somewhere, then use that file to do an unattended installation, you can google how to do it, I did a quick search and this is some random page with instructions (you can skip the steps they guy uses to locate the file, also you can skip the part to make it silent if you still want to have input on the setup) Doing this will get you the same setup as you already had http://mssqlfun.com/2013/01/29/sql-server-silent-unattended-installation-using-configuration-file/