Changes to wp-config.php

I have been managing my WordPress blog for several months now and wanted to get it running faster by emptying the cache. I installed a feature that prompted me to add code to the wp-config.php file through an FTP server. I made the change, not fully knowing what I was doing, and my site appears blank. I reverted the file back, but that does not help any. I can’t even log in to the WordPress platform anymore. The entire website is blank right now.
What do I need to do?!? My site is completely dysfunctional at this point, and I need to get it running again ASAP!