my meta description/tags on homepage have disappeared. Help please?

Something odd has happened to my search results and meta tag.

I was ranking quit high for the term ‘how to quit your job’, I did this legitimately without using black hat methods but suddenly I’ve dropped down from top 100 to about 300.

The thing is, when I eventually find my search result listing, it shows the correct title but the meta description snippet has changed to displaying the first couple lines of my latest posts, instead of the meta description that it used to display. (written using all-in-one-seo plugin)

I have looked in the header.php file and there is nothing in there about meta descriptions.

I would like to add that search results for my individual posts are unaffected, it’s just my homepage meta.

Does anyone have any ideas what happened here and how to get it so it starts displaying my normal meta description again?

Thanks