Are you logging into an FTP account created within cPanel, or the actual main FTP account? If you're logging into one created within cPanel, you might need to use the actual main FTP account to access your public_html directory.
Do remember that this is quite important, however. If you are logging into an FTP account you created then this could be a potentially very easy fix that no-one will even have to give you specific advice over - just start logging on with your main FTP account instead of one manually created in cPanel.
