Hi, vdboor and all, thanks for your help, problem solved, it turn out to be my stupid fault, a week ago, my ISP's DNS had some problem, so I temporarily changed the name server to one I found on the web, it belongs to the Dell network , I forgot to changed it back. Just now I ran netstat and whois, surprisingly found that kopete and kmess wanted to connect to a server also belongs to the Dell.com. Now I've changed the name server back to the ISP's, everything is OK now. My windows box's setting didn't change so not affected.
Thank you all again, say sorry to Microsoft