Modem will not work after installing a router

Question

The problem is my parents have highspeed and everything was working perfectly fine until my dad tried to hook up a router to connect his second computer. All he did was plug it in. About a hour or so after plugging the router in the modem shut down. Now the dsl and internet light will not come on the modem. The power and ethernet light does come on. They contacted their provider and they sent them a new modem. They are having the same issue with the new modem. My dad had unplugged the router and tried resetting the modem and still no internet or DSL light. Could someone give me some suggestions or solutions on what to do about that problem? Thank you