Vista - Ethernet connection problems

Hi,

I recently bought a new computer with Vista on and the ethernet connection was working fine for a few weeks now suddenly it finds it impossible to connect to anything properly using ethernet cable it seems to connect to my brothers router but not to the internet when i look it says that it's sending packets but not recieveing any so far i've tried a number of ways to solve this, i've also checked the cable and the router are working and have tried connecting my computer to my ps3 with the same results and i was wondering if anyone else has any idea what might be going wrong, thanks in advance for any help you can give