Update (31.12.2009): It can easily see that there are a lot of Windows users have been bugged by this error (this post has occupied one third of the total visits of my blog), and I hope this article can help to solve your problem. But please be aware though, all the solutions were gathered from internet, such as article, forum etc., and I can’t guarantee that they will work for you. If they did, you are always welcomed to reply and let people know what have you done to solve your problem. Else, I am sorry that I couldn’t help you, perhaps you can ask for help from your ISP. I have updated several more possible solutions based on some readers’ replies.
You try to initiate the broadband dialer in Windows 7 and only found that it doesn’t work and returned with an error 651: Your modem (or other connecting device) has reported an error. And you had tried to restart your PC, your router, your modem etc. and the problem doesn’t go away. And eventually you want to bang your head to the wall because you can’t solve the problem, nor you can find solution online because you are not able to get online!
Same thing happened to me last few days which caused the update of the blog delayed. During some normal surfing, I found out that the connection was hang, thus I just disconnect the internet connection and try to reconnect. But hey, I can’t connect back anymore, with the error 651 while everything (hardware, Windows etc.) were ok. So for a few days, I can’t update my blog and I was trying to find solution for it in the office (don’t tell the boss, won’t ya?).