I have a website with a url http://site.com but i think the sub domain http://[B]here[/B].site.com is causing the main site to drop in search engines.. is this possible? how do i hide the sub domain from bein indexed?
If the subdomain has more back-links, or is deemed more relevant for that search query by the search engines, then yes - it's likely to out rank the non-subdomain site.
Do you really want to block it? If so, just use robots.txt in the root of the sub-domain to prevent it from being indexed.