Is it a new site?
Are you adding new content to it?
Is it a blog style site with a front page that changes often?
If a site is new (up to a few months) then it will bob about as Google decides what it should rank for.
By un-indexed do you mean really un-indexed or just not showing for the keywords you expect it to rank for (they are completely different things)
do a URL: search for your site - if it appears - it isn't un-indexed.
Remember - Google decides what your site ranks for not you. You can persuade them subtly of course (which is what SEO is) but you might be ranking for words or phrases that you really don't expect to when a site is new.
Particularly true if you have a blog roll on the front page and it changes all the time. To begin with this really confuses Google (I mean blogging is only 12+ years old and done by millions of people - you wouldn't expect a multi billion dollar corp like Google - whose JOB IT IS to understand web content to have worked this out yet would you - nah - there's no money in correctly identifying and ranking new blogs with blog roll front pages - so Google don't spend one second or one cent even trying.. Googles motto:
"If you've got no cash? Then we can't be assed"
Getting some links, adding content of a similar nature - interlinking from your own sites other URL's with appropriate keywords, using appropriate ALT tags on images and getting the meta data sorted out, getting some inbounds with appropriate anchor text... the usual
Good luck