Is it possible only adding original content? Can I join some blog networks like MyBlogNetwork or similar to have content or I'll lose the PR?
Haha, well, if you recreated all the content you could possibly keep it's PR. The only reason Google gave that website a particular PR is because it thought that website's content was useful/terrible! After Google realizes those pages are gone and Google updates it's PR rankings your PR is gone. I'm really sorry to tell you this.
If it is a blog and runs on wordpress you can install a plugin called 'link juice keeper' it is free and will help you to preserve the link juice of backlinks that are pointing to pages and posts that don't exist anymore. Make also sure, before you buy, that the pagerank wasn't faked in the first place, SY
Go for fresh content and after it ,generate some back links for your website. by doing link building and submission.