Hi TiPod, and welcome to the Vista Forums
As a first check double click on the Red X to let windows diagnose the fault
if this fails ...
One thing you could try is to do into the Device Manager and un-install your network driver, reboot and let windows re-install the driver, this is probably the quickest method to reset the device to defaults.
when you are at the default state check the settings for TCP/ip interface on the room-mates (working) system and set yours to the same (obviously if this is set to a fixed IP address then you need to set this to the address allocated to you)
I would normally advise a system restoe for this type of error but if more than a few days have passed then this cause even more problems