Problem with installing plugins and themes

I’ve just downloaded and installed new 3.0.1 wordpress. I have set 777 rights on all the folders. But I’m still can’t install anything. When I’m installing theme or plugin, after i enter all the ftp settings (host, usernname, password) I click “next” button and then main frame become white and nothing happens. No error, no bugs, no crashes, just nothing happens. I’ve tried to upload theme to themes folder manually – it’s ok, but in admin panel in themes tab it doesn’t appear so i can’t use it! What’s the problem? I’m sure that ftp host, username and password are right.