Resetting the TCP/IP stack on Wndows 7

This computer occasionally inserts a new gateway ip address into the ip configuration that prevents the NIC from seeing the router.  At the moment, it has been set to 0.0.0.0, with the proper address - 192.168.1.1 - listed second.  Last week, it was set to an address that turned out to be one of my ISP's public domains.  Manually setting the addresses in the Local Area Network settings box does not remove the offending addresses, only adds the new ones to the end of the list.  I have to resort to bypassing the router completely and plugging directly into the cable modem, a method that is extremely irritating to everyone else on my LAN who lose their shared internet connection while I do.

My ISP suggested a corrupted tcp/ip stack, but their link to a Knowlege Base article on Net Shell commands was for Windows Vista, and had a warning that that article did not apply to Win 7.  So far I have not found the Win 7 version of that article.  Can someone point me in the right direction, or suggest another cause of this problem?  If I do nothing, the problem will resolve itself magically in two or three days, but if I shut down, the problem will resume when I power back up.

This is a two-month-old Dell Inspiron with an Intel Core2 Quad processor, running factory-installed Win 7 Home Premium.