Unable to Upgrade: Upgrade page not found

I used Dreamhost's One-Click Install to install Omeka 1.3.2.

I then followed Omeka's instructions for upgrading to 1.5.1.

When I web-browse to my admin panel (and am supposed to be redirected to upgrade database), I am redirected, but I land at a 404 error:

"The requested URL /nt/admin/upgrade was not found on this server."

When I try to go to public page, a message displays:

"Public site is unavailable until the upgrade completes."

Can anyone help?

Make sure you've got all the files from the Omeka zip uploaded correctly.

In particular, this sounds like the kind of problem people often have when they're missing the ".htaccess" file that should be in the top-level Omeka directory. That file can often show up as "hidden," so you might have missed it.

Thank you so much, John! You know I read other people having a similar issue, but none described (I thought) exactly what I was experiencing...your indication of exactly WHERE to look for the .htaccess also helped immensely. Thanks again.