So my final solution is to ditch the old domain name, create a new domain name and recreate new content for my client.
In just 3 weeks, my client's website are now ranking in the first page.
Now, that leaves me with a question about my old domain name. I want to do a domain 301 redirect to pass the PR/DA/PA to my new domain name.
I have never done this before so I wanted to know what attributes are really passed to the new domain name when I do a 301 redirect? Is it only just the PR/DA/PA? Or more attributes are passed like penalty, etc?