I started a website before 7 months. The site has 1500 pages and all of them are with unique content. When i put it online google index 1400 pages, then after 2 months de-index a lot of pages and now they are only 550... WHY ? Also the unique content is not indexed too. What you think ? Is is possible still to be in the sandbox? Or may be need some linkbacks or more time ?
There are too many reasons why it could happen. Its impossible for anyone to tell without actually seeing the site.
Sign up with Google Webmaster Central how you can track the status of your site(s), including crawl errors, crawl rate, etc..
yes, Google Webmaster Central might give you some answers, and also may be Google doesn't like how long/short are your articles and thinks it's a spam site..
from 1500 pages to 550? oh, almost 63% of your web pages are not indexed. well, google as far as i know is the strictest crawler among any others. just a single suspicious thing in your web page, it automatically remove or excempt that page from indexing. you might not be aware that your 950 web pages are guilty of keyword stuffing, cloaking, or been having lots of javascript (that is, spider can't crawl on pages with javascripts on them).. your keywords must not exceed 9% percent of your web page content. ideally, it should only be 5% keyword density. also, you might have link to link farms that appears like directory sometimes.or, you must have linked to sites that are linked to sites that are doing casino, porn, or selling pills. then, those web pages must be spams in a spider's mind (if it has a mind.actually, it's algorithm.)
use sitemap and this sitemap in Google Webmaster tools. Also create Robots.txt file & in this file mention your sitemap path. Like this example of robots.txt file: User-agent: * Disallow: sitemap: http://www.yourdomain.com//sitemap.xml
use xml sitemap and submit this to google webmaster tools and use http://www.google.com/analytics/#utm_campaign=en&utm_source=en-webmaster_central&utm_medium=et to track your site
1500 unique pages in 7 months? thats more than 7 unique pages of writing per day, 7 days a week. must be your full time job. how many backlinks you have? do you have a sitemap?