Thanks a lot for you attention and patience.
Let me make myself more clear.
English is not my native language and I have some problems to make myself clear sometimes.
It's expected. Not a problem.
The problem is:
I can access the blog without any problems through URL http://www.miacao.org/wp . /wp is a folder/directory at root of my hosting plan. Blog is almost ok. So I created a subdomain called miablog.miacao.org that points to that /wp directory.
Like you must know, at WordPress main directory we do not have an index.html. We have only an index.php, that is executed when http://www.miacao.org/wp or http://miablog.miacao.org .
With http://www.miacao.org/wp it's all ok. The blog shows without any problems.
With http://miablog.miacao.org index.php don't do his job and redirects to http://www.miacao.org. Like I said above, that is being redirect to http://forum.miacao.org, so you finnaly goes to that url.
I had a big and unfair fight with my hosting support. I was blamming them, telling that their subdomains system was kakked. But I was completely wrong. They did a simple test that proves to me that the real problem was the WP code. They put an index.html at WP directory and sobdomain works fine.
So, the problem is someplace of WP code...
When I did what you suggest before, I cannot access the blog. To access it I had to take the absolute path to wp-login.php
And now? What can I do?