Many of the low-cost hosting services use what is called Virtual Hosting (or sometimes Sub-hosting). Virtual Hosting is made possible by the introduction of HTTP/1.1 of the NCSA server, allowing multiple domains to be hosted under the same IP Address or virtual server. For example www.domain1.com and www.domain2.com would both point to the IP address 187.230.120.85. Many of the $10 to $50 per month hosting options fall under this category, with many sites sharing an overloaded server with the ISP or hosting company's web site.
What this means is that visitors using older browsers and some search engines will not be able to see your web site, since it would point to your ISP's web page. There are also other disadvantages to Virtual Hosting as explained here.
To test your domain, enter it in the box below. If you site is not hosted with it's own IP address you may wish to upgrade to a Virtual Server.