A lot of DSL modems actually have routing functionality that interferes with your actual router. They tend to use a PPOE setup, which means you have to tell your modem to not do PPOE and use the settings that it had to tell your router it's a PPOE connection, complete with the login user/pass and external IP address the modem was getting. I know that sounds complex, so maybe just google on that subject with some keywords and you'll likely find the steps for it.
When I'm Word for an extended period of time, or a graphics-heavy page (i.e. Facebook), my screen's image breaks up with a number of red lines. It's like that scene in Matrix when the screen goes all green, except in this case it's red.