if i had to guess at anything i would say you have a router. The router must be issuing and ip address for the mac address of the network card and when you boot into another os your getting a conflict. So i would check that all 3 are set to dhcp (router,win,osx) or at least win and osx have the same static ip address if its set manually. I usually just set all to dhcp but tell the router to reserve ip address according to the mac address. If for some reason osx is coming up with a junk ip address just set all the details manually to match what you have in win.

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