I have the most recent version of Zen Cart (installed it a few days ago) and I have no add ons

I *have* made changes to some core files (deleted the advanced_search.php due to restrictions by my webhost and edited the english.php file under /includes/languages/ for a few aesthetic things, but past that really nothing)

What's currently going on:

After the completion of any form on the site (register, log in, unsubscribe from newsletter, etc.) instead of returning to the home page or other relevant page, it displays a blank page and the browser asserts that it is done loading. If I manually return to the main site, the form is always completed successfully, it just fails to return you to a page which displays information.

I'm worried that this may extend to things like the shopping cart or checkout, but I haven't gotten to creating a product list, so there's no telling yet.

What could be causing this? Is there a sitewide function for redirect on completion/submission of a form? Does each .php file have it's own unique redirect code? What's going on here?

Halp!