No effect on web after editing CSS WP 2.8.4

I started hosting a new web using WP 2.8.4. It is not my first time using WP.

But when I edit the CSS template, I find something wrong. The CSS file is updated after saving, but there is no effect on the web. But when i edit header, index, sidebar file with extension php, the effect is directly after loading the web.

I have erasse the cache, temporary file etc on my firefox, but there is still no effet. I try to use IE, Flock and Safari browser, but all give me same result……no effect at all.

Any suggestion why this CSS file trouble happen?