duplicate content issue - what is the solution ?

I have created a website. its a month old. my website got indexed and after some time i changed the page title. i checked my website in google and i saw duplicate titles, Now in google my webpages have new title and old title, old title showing 404 errors. is it really bad for my website.

how long will it take for google to remove those old indexed page title ?

what should i do to remove the old titles ?

Do you think that my website is punished by panda because i see my website nowhere for the main keyword i am ranking even its a emd domain.
i can see crap websites on the first page. even the video added by me with the same title with back link to my website is on the first page.
my website is on the first page for yahoo and bing but nowhere is the google. i have added some web 2 backlinks in the last two days but no results.

I've exactly same issue

maybe it just needs to be recrawled?

any expert please

Just rebuild your sitemap once and next time when google bot visits your site its should gradually remove old titles from search

I don't know about it? But my friend is known this side. Thanks

Do a 301 redirect on the broken links (404).

You can just ping your website again and again and just wait for the Google bot to crawl your website.