Thanks for such a quick response. This is my very first Support question so I really don't know if I should start a new thread or not. Now I know.
I am on OS X 10.9 and should use sudo killall -HUP mDNSResponder instead. I can ping now but still can't open in a browser. I'll wait for a few hours...
I seem to have the same problem with domain cccc.x10.bz. It worked before. I did the DNS Flush with dscacheutil -flushcache but did not help. Can you look into it? Thanks.