I don't mean to insult your intelligence, but I must ask you to please explain exactly what you did in order to establish your local site.
You've clearly missed a step, and it appears to be a result of either not reloading the data to the database, or you are pointing to the wrong table-prefix.
fix_cache_key deals with fixing login problems.
It should never show up as a blank screen. It really requires no instructions. They are all on-screen when it runs, and basically all they say is to delete the file after running it, because it auto-sets the required setting to the database if it can connect successfully.
As for documentation, it's inside the fix_cache_key.php file on lines 24-37. I've copied that content below for easy reference.
Maybe it's showing up blank because the database data in your configure.php is bad and it's croaking because it wasn't written with the expectation of bad setup.
ALL it does is read the configure.php file to select database settings and connec to the database, and then edit the "SESSION_WRITE_DIRECTORY" record in the configuration table to match what's set in your configure.php file for DIR_FS_SQL_CACHE. You can do this via phpMyAdmin yourself ... the fix_cache_key tool is just a simpler way to do the same thing.
Again, it has nothing to do with having no data show up in your store. That's a configuration problem in your configure.php or the result of a truly empty database.
/*
- This utility is used to reset your "SESSION_WRITE_DIRECTORY" key after switching servers.
-
- Make sure the DIR_FS_SQL_CACHE setting is correct in your /includes/configure.php file.
-
- Copy this file to the folder where "index.php" exists for your Zen Cart site
-
- Run it
-
- The cache setting from your configure.php file will be displayed, followed by
- the cache setting from your database.
- If they match, it will say "No changes required."
- If they do not match, it will synchronize the database to match the configure.php setting.
-
- VERY IMPORTANT .... WHEN DONE, DELETE THIS FILE FROM YOUR SERVER!!!!!!!!!!!
- If you don't delete it (or at least rename it to something very obscure), then you run the
- risk of somebody using it to find out information about your server configuration, which
- could compromise your site's security. Thus, deleting this file when finished is the best approach.
*/