Forum Moderators: Robert Charlton & goodroi
Posting personal URLs is not allowed under the WW ToS--a moderator will likely be along shortly to remove the link. :)
Also, you might get more relevant responses in the Google-specific category.
This could be any number of issues, from Google re-spidering your website or your competitors' websites to even receiving a penalty for perceived "black-hat" (what Google sees as unethical) optimisation techniques. I'm no expert, but a sudden drop like this generally implies some sort of a penalty to me.
Eg, is the site simply not ranking, or has it disappeared from the index? Have you tried using the site: operator? Have you searched for exact text strings from your page?
Where is the site hosted? Is it in English or Greek? Are your inbound links from .gr sites, or from .coms?
In the Hot Topics [webmasterworld.com] section, pinned to the top of the Google Search forum home page, there are several sections that might apply to your situation that you should check out. Look at these sections in particular. Which is most applicable will depend on the nature of your problem...
- PENALTIES, SANDBOX & TRUST
- GEO-TARGETED SEARCH