Everything 404, including CP login, please help

I'm not sure what to do. I installed the SEO4SMF package as per the instructions but instead of changing the default URL which would have been

forum/index.php/topic,24.0.html

after I enabled the mod, I get

forum/index.php/ACTUAL-NAME-OF-TOPIC,24.0.html

and because it stills keeps the ",24.0.html", I got a 404.

I couldn't figure this out so I removed SEO4SMF temporarily and tried the Pretty URLs mod. That worked for a minute or so but then when I checked my remote files I saw that SEO4SMF was still in there in bits and pieces and then Pretty URLs was giving me a 404.

Then I was checking the threads about mod_rewrite being enabled so I wrote to my host about this. Without warning me about this in advance they added an htaccess file in the forum directory for SEO4SMF although I had removed that mod.

Now I have an htaccess file for SEO4SMF in place although the mod was removed; and I get a 404 for everything including the login page for the SMF control panel.

I have no idea what to do. Can anyonen help?

The host wrote to me saying

mod_rewrite is indeed enabled on the server and your account.
I have set the requested .htaccess file in the forum/ directory but it's still not working as requested (has to do with the actual rewrite rules and not the mod_rewrite module).