If you feel that everything possible has been done to your web site to meet all high search engine ranking criteria and you still do not find your site ranked at the top of search engines, you web hosting service may be to blame...

How Can My Web Host Affect My Rankings?

If your server is not guaranteed to be up 99.9% of the time, there is a good chance your site will be down when a spider or editor visits your pages. If your site is not viewable, it could be detrimental to your rankings.
If you do not have twenty-four hour access to your files, this will eventually slow the optimization process of your site.
Free hosting services can be slow, often require pop-up ads and experience frequent down time.
There could be numerous banned web sites being hosted from your server or from the very same IP address that your site resides on.

What You Want In A Hosting Service
For Successful Search Engine Optimization...

A unique I.P. address for each of your sites. (There is some controversy over the necessity of this, but we highly recommend having a unique I.P. address for each site and that you are sharing your I.P. with no one. If you are sharing your IP with multiple sites, the search engines could automatically ignore your site if there have been many incidents of spamming from other sites using the same IP as you are using.)
Guaranteed 99.9% up-time -- Be sure to monitor this.
A service that allows you twenty-four hour access to your files.
The ability to up-load files at YOUR convenience.
Technical assistance that is available at least during business hours on normal occasions.

Following the above tips will give your site one more added boost to increasing the accessibility of your pages for better indexing and ranking potential.

Source : http://www.internetmarketingwebsites.com/web-hosting-search-engine-optimization.htm