Changed site to network, problem …

I just changed a wp install into a multisite network, doing my best to follow all directions for a subdirectories network, not a subdomain network.

When the install finished and I accessed the superadmin to add a site, it asked for the subdomain name, etc. So, I changed the SUBDOMAIN_INSTALL to false in the wp-config, deleted the added site, and tried again.

Second try seemed to be working correctly, until I tried to visit the site. It has no CSS. Site options lists css and template, but it appears to have no theme. Also, I get a 404 when I try to visit the new site’s wp-admin.

Please let me know what mistake I made. I’m expecting that it was somewhat routine, as I’m not a pro.

Thanks!