One of my sites has been sandboxed by google couple of weeks back and it happened before so I've sat 301 redirect from http:// to http://www. and my site came back but with this one I've change the content added more content but its still not out of the whole will switching the domain name help me getting out of sandbox and will I get my old ranking ( I was on the first page of G), please advise. Thank you!
You probably won't get back your old ranking, but something close. I'm not sure, haven't tested it out before. It might also be that Google doesn't count backlinks from sandboxed pages. You'd have to try it out. Also, I suggest searching a bit for threads on getting sandboxing, there's been quite a few people who just kept adding backlinks and it eventually came out in an even better position.
I wouldn't do that. Wait it out and keep building links. Your site will come back stronger than ever if you follow the advice all around this forum.