hello. One of my website is not cached from Google from last week on which I have changed the Title and META tags on 31st Dec, 09. What could be the reason?
Alone changing the title and meta tags wont help you to cache. You need to do link building(Do follow social bookmarking is better) for support them to cache.
Cache appears when you site is indexed. If you are not cached it means you have no backlink. And I guess you meant a page not a website , because every website has many pages and each page may or may not be indexed.
Does you site publish new content? If yes, a few links from forum signatures or social bookmarking sites should help it get indexed.