Today my website suddenly lost its ranking and got uncached by Google. Anyone can tell me why this happened?

[Jeff]

It's possible you have some bad SEO habits.

Google has a reputation of dropping sites if they think your site popularity is spammed. For example, if you over do it on keywords or use keywords that don't actually pertain to your content, you could be tagged as a spammer with your site. Another thing to consider is where is your site linked?

If you try to get more visits by being added to a "link farm" or you find a source that will "increase your visits", that could create a bad rap with Google as well. Especially if the number of visits jumps a huge amount in a short period of time. You should also research SEO services before you hire them to improve your site. Some organizations will cheat you out of a good reputation with Google just to get a quick sale with you.

Last thing I could think of is if your site is up to date or not and contains relevant information. If your site never shows signs of life via new content, you also will loose popularity. Keeping a well maintained site will also help keep your site in the Google spot light.

Check out my sources listed below and read these articles to help clarify what to look for.