DSL works by sending information over regular phone lines at a higher frequency than regular analog signals, resulting in faster Internet speeds. However, DSL, like any other Internet connection type, is prone to errors or failures. In addition, you also may not be getting the speed that you signed up for. Either way, you may want to test it to find out why.
Access your modem's settings by typing the IP indicated in your modem's manual. Most DSL modems include the ability to test their own line from within the modem, allowing you to diagnose whether the problem is your modem or the DSL line.
Use an online speedtesting service such as SpeedTest. If your problem isn't so much getting online as it is seeing if you're getting the proper speed, Speedtest can run a test and show you what your average speed is, in order to get your money's worth from your ISP.
Have your ISP's technical support test your modem from their side of the connection. Most technical support agents can test your modem's connection and speed, and if they find the connection lacking, can assist you in getting it back in shape.
Use the DSL Reports Line quality test to determine if your DSL problems lie in the actual transmission of the connection, as in "packet loss, excessive latency, or internet or ISP congestion." The system will ping you from two different servers to determine if there is a problem in transmission.