i had a probelm similar to the ones you guys are listing, more a combination thereof. basically my IP had changed on my PC, with no physical changes to the network. none on the network had any access to the internet however. basically, all i did was. shutdown everything, starting with the PCs and working my way up: switches, router, modem. and then waited for about 15 mins and plugged it all back in in reverse order. modem, 2mins then router, 2 mins, then switches, 2 mins then PCs and laptops. now it works fine. its a wired network by the way.