I had H1b from Aug 2001 to Aug 2004 and then from Aug 2004 to Aug 2007. In Aug 07 my employer transferred it to L1A. So far, I have spent 4.6 yrs in US. Can my H1b be revived/reactivated? Change I switch job?

As long as you don't exceed the limit and you employer is willing to sponsor you, it's fine.