If it is occurring on both yours AND your room mates computers, You can bet ur arse its not Computer related... Somethings gone wrong with the router... Take note of all your Connection settings on the router configuration page and thgen re-set the router to defaults.
Re-configure your connection settings (there is often a back-up and restore option to make this simpler) Then give it a bash... If that doesnt work... and you can prove there is nothing wrong with the line, you need yerself a new router sonny boy!
[EDIT]... My bad... Just realised you said the others ARE working lol...
What OS are all the 3 machines running?
Are you using a Static IP?
Go into your Adaped properties, Configure your TCP/IP settings so that the default gateway is looking for the router and not some far off land
Default Gateway: 255.255.255.0
Default Gateway: Router IP