Internet Problem.

I Just installed the latest windows 7 Ultimate. The only problem I have is, the internet connection. It functions well for just an hour more or less, then, all of a sudden, no warnings are given, just the firefox wont run anymore,the messenger doesn't sign in, and the internet explorer keeps trying to connect to the website given, as if there is no internet connection, while it says that I am still connected.
Anyone has an idea to fix this problem??? I tried installing the network card and even disabling the firewall, as yesterday the utorrent continued downloading and the xfire kept on working normally but the firefox, internet explorer and messanger didn't work, any help??

my mother board is asus P5N73-AM , and the chipset is nForce 610i with an on board network card, and I use a cable connection, need help!!!

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