With DSL connection issues, there can be multiple points of failure. It is important to work in such a way that you isolate the cause of the problem.
Your first step in trouble shooting should always be to powercycle your modem (and router if applicable). This means remove power from the device. You will want to unplug the power cord from the modem for 30 seconds, then plug the modem back in. This forces the DSL to try to re-establish your connection. Many times merely powercycling will bring the service back up.
If you have a Router, you will want to powercycle it as well after you have powercycled the modem. You will want to be sure that any ethernet cables are connected securely.