Well, the upgrade steps have you exclude several files and folders for an upgrade which contain your unique configuration; the includes folder for example has all of your board rules, config, coppa, header, footer, forum introductions, sharaholic information, privacy policy, etc. If you overwrote them you'll want to restore the folders you should generally exclude from an upgrade.
A new install comes with several files which will overwrite the includes folder if the upgrade instructions aren't followed; these files in the 7.7.0 release are:
cache_builders/custom/*
includes/boardrules.php
includes/closedforums.php
includes/community_intro.php
includes/config.inc.php
includes/coppainsert.php
includes/footer.php
includes/header.php
includes/header-insert.php
includes/privacy.php
styles/wrappers.php
