Missing structures, can't set permissions in 3.0
I have been successfully using a 2.x version for a little while. It was loaded via my web host's fantastico system. Fantastico recently advised me that there was a newer version (3.0) and did I want to upgrade. I said yes. I now have a database incompatibility although all pages are accessible by one means or another. I cannot access the installer - I am told I don't have permission, and my web host is unable to help in this instance.
After much fruitless searching, I decided to try creating a new 3.0 installation as originalUrl/wiki. That loaded successfully and I have transferred all pages (there weren't too many) to the new wiki.
The problems now are:
1 - that I cannot get Structures to work. I have TOC enabled, but the Structures menu item does not appear.
2 - I cannot set permissions for a newly created group. Everything I tick just disappears when I hit the ?can't-remember-what? button.
3 - The left bar containing the user menu disappears for an anonymous visitor.
Suggestions gratefully received.