Hi Aderson.
I finally got to the bottom of this. I went back to the hosting co powerdnn who said
DNN 7+ has a minimum requirement of Windows Server 2008, IIS 7.5, and .NET 4.0.
The server your site is currently hosted on is a Windows Server 2003 server, withIIS 6.0.
I migrated the site to another server and everything is working fine now.
I had seen the issue reported a couple of times so this might help someone :)
best wishes
sharon