I thing google update their rankigs time after time or it's just other sites raised their rankings rapidly
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חינוך giochi online

Did you make any change in your website? Like change the Title tags etc.

this effect rankings temporarly unless things are changed completely.

Assuming its new site this happen it appear and disappear, might be google updates it's technology beyond the normal monthly updates, does it appear in other search engine like MSN & Yahoo! ?

I don't think thats the reason for site disappearing.

The major factor is when you make changes to your website. The result can be dropping in rankings and it usually takes several weeks to regain rankings or see increased rankings.

This is not uncommon for Google. Especially for new sites. If your rankings aren't restored within a couple of weeks it is safe to assume they aren't coming back any time soon. You will have to do what everyone else does to improve their rankings: keep adding unique quality content and promoting your site.

Additionally, Yahoo and Google rarely have similar results. Their algorithms are very different at the current time. So you can rank well in Yahoo and do poorly in Google.

Beside content quality backlinks will also help.

Actually, the point of quality content is to get quality backlinks. You can't get a decent number of quality backlinks without quality content.

From 1st January 2007 there has been reports of sites losing ranks in Google. Looks like a google algo tweak. If you have not done anything bad (spammy?) in your site, then it might be worth waiting for some weeks to see how things develop. I have seen and managed sites coming back strongly after losing rank for 3 - 4 months.

Remember, for every site losing rank there is another site gaining rank. This is normal. After all, how do you know that the sites gaining rank don't deserve to be ranked higher?