I have DSL downstairs and had a contractor extend the phone line upstairs, but he only wired the upstairs jack for phone, not DSL. I had to connect the available wires in the line to the (two) appropriate wire terminals in the DSL jack.
The following information in this forum led me in the right direction to fix this, but it turned out that the color matching for my DSL wiring is different. It probably depends on the type of line. I've crossed out and updated what I had to change in my setup.
WIRE COLOR42A BLOCK
RED OR BLUE WITH WHITE STRIPE RED
GREEN OR WHITE WITH BLUE STRIPE GREEN
YELLOW OR ORANGE WITH WHITE STRIPE GREEN* YELLOW
BLACK OR WHITE WITH ORANGE GREEN STRIPE BLACK
* The instructions I found indicated Green with White Stripe for this, but I only had Green available, and it worked.