I have a website with a Page Rank 3. Yesterday it was listed in Google as the second link (under a specific Hebrew keyword). 12 hours later I checked it with my Google Monitor tool and it seems my website doesn't appear in Google search results anymore.
closed as not constructive by Stephen Ostermiller, bybe, Su', Christofian Mar 8 at 3:38
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Definitely do what Sidg suggested and sign up for Webmaster Tools. This is your direct connection to Google in relation to your site.
To answer your question, it could be something as simple as Google's results haven't synchrnoized across all of their servers and datacenters yet. Google's servers span many different datacenters and your site may be ranked in one and non-existant in another. You said your site only ranked yesterday, give it some time and monitor the changes with Webmaster Tools.
Login into webmaster. Goto Health and check if there is any error.
Also share the domain name.