missing posts

Hi
Just noticed 10 of my posts are missing, I discovered while using googles webmaster tools and got site crawl errors showing 404 results on ten posts, i did change my theme a while ago,i didn’t delete any posts though. The posts don’t appear in my dashboard, just wondered if I can get them back, if not how do I stop google showing them as errors.
ps im not an I.T idiot but a newbie on WordPress

Thanks

Chris