Hello, I am a new user, I checked other thread any to my best knowledge there is no topic like this one elsewhere.
I bought Nokia N9 on ebay in mint condition, I was using it for 4 or 5 days and the on the 5th day, all of a suden blocked itself. I now won't read any sim card and usb cabel, it just keep asking for an unlock code, which I don't know. I asked previous owner, but he doesn;t know the code either, he said he restored fatory setting before he send the phone to me.
Is there any chance you could help me ?

have you tried 12345?

Also try this : http://talk.maemo.org/showthread.php?t=89471

worst case if of couse that its stolen N9 sold in ebay, and the real owned did remote lock on it. In which case we shouldn't be helping you. But as you already find the way in here, you can surely use search in this forum, it has flashing instructions of howto clear unlock code to factory state.