The problem is that whenever I open some new website, even just Yahoo or Google, it took an hour just to load the page, it's very slow. I tried to install the "security guard 360"(I'm sorry that this is in English, my compnay's computers don't have a Chinese output.) mentioned in FLYWXC's post below to clean it up, but my computer was too slow to run it successfully.
Thanks again for your help!