Desperately Need a Help related to computer and Internet

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I am getting an error message and it is - "There is an IP address conflict with another system on the network". I want to know why is it happening. I use internet through a broadband cable modem and there is wi-fi in it (However, I don't use the Wi-fi). And My laptop is not connected to any other machine. Please tell me why is it happening and how to resolve it? Also, Is it dangerous in security point of view? I mean is it possible that somebody else is using my Internet through wi-fi? However I have a user name and password which I have not told to anybody.. Please Help me! I am worried about it. I also googled about this problem and there was some answers but I didn't understand them. So Please explain me in easy and simple terms.. Thanks in Advance..