You can start over by dropping all of the tables to the database ... be sure to backup in case of a problem ... then reloading all of the files via FTP ...

I am not seeing anything obvious here ...

I might suggest that you look at the newest release:
http://www.zen-cart.com/forum/showthread.php?t=69769

if you are going to start over ...

And you might try first loading all of the files again just to see if that is all that it takes to fix the problems you are having ...