blackhawk

At the small business I work for, a DSL connection is provided via a
2wire dsl router and Linksys hub. This network works just fine, except
when a colleague tried to add another computer at his workspace. He
extended his port with a router and both his computers were working
fine..for awhile. Soon, the entire office's internet connection became patchy and then dropped entirely. Looking at the 2wire router, one can see it power on and then immediately power off again. this power cycling continues.
When he replaced the router with a hub, the network seemed to remain
stable for a longer time, but it eventually caused the network to power
cycle repeatedly. Any idea what is going on? and how the network can be expanded at my colleague's workstation port?