Hi, thank you for your replying.
On my live site, readtheweb.info, I only activated one plugin, that is the Language Switcher plugin.
After I disable the plugin, that is, no plugin enabled on my installation, the titles on the single post page and static page are still didn't show up.
And yes, I have tried different themes, the two default themes comes with WordPress, and the theme I use right now. And on my live blog, I didn't install the optimal-title plugin.
If you need some information for helping your ID the problem, what else could I give you?
Before upgrading, everything is fine. Remeber, I did fresh install on my home PC, not upgrading, but it is the same.