recently i have my own blog, but with an old domain name. and the site was a credit card site before, with PR2. when i site it in google, i found both the old information and the newly blog post. I want to know when google next update the PR, what would happen to my site?
If it has completely different content now to what used to be on there then its going to eventually lose backlinks and pagerank and possibly any traffic that was still trickling through from old searches.
pr wise I guess its no problem. SE ranking is what I think will have effects specially if your new blog is of different niche.
As long as your backlinks stay in place (many sites don't keep a check) then your PR should stay the same, but remember PR only is a very small factor in ranking position - you will only rank well with good quality content and relevant backlinks. If the domain was dropped that will affect things alot
Does the domain name have old links? As in links that have been around for years? If so, rock and roll with it. Google loves old links, it loves old sites, it even loves old sites that have been up and down and all around. Last year I picked up an old domain name that had been expired for about 3 - 4 years. The good thing, it has backlinks that are over 10 years old. As soon as I put the new site up, google grabbed the pages and indexed everyone of them. It was like the site never missed a step in googles ranking.
All of your information, description, new tags, keywords and such will eventually become the new blog. I just did the same thing, and it was updated almost immediately (the same day). Any links to posts are gone, (since the posts are gone) but you may still retain home page links, although your anchor text links won't help you with your new keyword target. The worst that could happen is any post links will divert to your 404 page. It may be a good idea to customize that a little and tell about the new site.