Problems with a Broadband line can be difficult to diagnose, although on the face of it, a simple phone connection, a successful Broadband connection involves software on the computer, working filters and Modem or Router, a good phone connection to the local exchange, the equipment in the local exchange needs to be working and have a link to the ISP who needs to be able to verify the connection (user name and password) and be connected to the Internet.
When the Broadband connection fails, it is helpful to find out what part of the system has a problem. It may be a general problem with the ISP that will be found and fixed or it may be a problem with the line or equipment at the exchange that won't get noticed until someone (you) reports it. It may also be a local problem with the filter, modem/router or computer setup.
The first step is to check the lights on the modem/router to see if they are indicating a DSL line. If you are using a modem, then there is usually some software or an Icon on the screen that indicates the link to the exchange is a good one.
If using a router then it is usual to be able to access the router's status and settings pages via a numeric web address ( such as http://192.168.0.1 ) the actual address will depend on your router and should be in the instructions that came with the router. Usually, the router's address will be the same as your computer's address with the last number changed to a 1 (so if you computer has an IP address of 192.168.1.3, the router may be found at 192.168.1.1)
You may also need a username and password to access the router's status and settings pages. If this has not been changed, you will find these in the router instructions - if these are not available, you will need to use another internet connected machine to look them up on the web. Be sure to have both the make and model of the router. If your router was supplied by your ISP as part of the Broadband connection, a call to their help line may be the quickest way to find the default username and password.
If you can access your router (or modem status software) It should indicate what is happening on the line. It should be finding a DSL line, making a PPP link and recieving an IP address.
If no DSL line is found, check the connection to the line and filters. If all looks well, (and the phone line is working for telephone calls!), try swapping the filters so that the modem/router is using a different one.
Try also removing the Modem/Router's filter from the wall socket and turning off the computer / router. Leave them turned off and un-plugged for 15 to 30 minutes. This will possibly 'unblock' the equipment at the exchange and give it a chance to notice that the line is disconnected. Then plug it back in and switch on - sometimes this is enough to clear a fault.
If the modem/router finds a DSL connection, but is un-able to start a PPP link, it may be that there is a problem with your password. If you are using a router, it is unusual for this to change, so it is probably time to contact your ISP who should be able to see your router's attempts at logging in and be able to correct the problem with you. If you are using a modem, check the connection software is still using the correct user name and possibly re-type the password, again, if this fails, you will need to contact your ISP.