When a DSL Internet connection goes down it is not always an issue with the service provider. It can often be a problem with customer's equipment such as a modem, router or any part of the Local Area Network.  Here are some basics steps to determine if the provider is at fault. These steps are designed for Windows and DSL modems in bridged mode. Mac users would use a different process. The basic idea is to eliminate the end user's equipment as much as possible and test if the connection works.

Verify wiring first. The DSL modem must be connected to the telephone jack on the wall via a telephone cord.  Ensure that the other end of the telephone cord is plugged into a telephone socket on the modem, not a network socket which is wider. Unplug all other equipment such as phones, fax machines, etc. from all jacks on the DSL line if the line is shared with other equipment. It is important to remove all equipment from the line except the modem as some equipment may interfere with DSL signal. If you are not sure if the modem is connected to the right jack verify the phone number of the jack by plugging a phone into it and calling ANAC.

Attach the power supply and plug it into a power outlet. If no lights are ON then check the modem for an on/off switch or button. Some have them some don't. Flip the switch or push the button to ON position. 

NEVER PUT A PAPER CLIP INTO A RESET BUTTON UNLESS YOUR SERVICE PROVIDER TELLS YOU TO DO SO. RESETTING THE MODEM WILL WIPE OUT IT'S PROGRAMMING AND THE UNIT WILL HAVE TO BE REPROGRAMMED. IF YOU ARE NOT UP TO IT THEN LEAVE THE RESET BUTTON ALONE.

If no modem lights turn on in a few seconds then your modem or its power supply may be faulty. If all modem lights are off unplug the modem and plug a desktop lamp where the modem's power supply was plugged in. Turn the lamp ON to verify that the power outlet has power. If the power outlet has power and all modem lights were off then  the modem and its power supply need to be replaced. 

If modem lights are on then the first light you want check is the DSL light. The DSL light indicates that the modem is in sync with another modem hosted by the telephone company. Some manufacturers fail to properly label the lights and use pictographs instead which make it very difficult to communicate which light is which when making a call to your service provider. The DSL light should be ON and solid. The light will blink before it turns solid and that is normal. A blinking DSL light or a DSL light that is OFF after 10 minute wait indicates a problem with the phone line, internal wiring, or the telephone cord. Check again the telephone cord. Make sure it is no more that 6 feet long. Then call your provider and report that the DSl light is OFF. Most likely they will dispatch a technician.

If the DSL light is ON and it is solid proceed as indicated below.

Plug a network cable into a network socket of the modem. Modems that have more one network socket may have them labeled as WAN nad LAN. Choose one of the LAN sockets. Plug the other end of the network cord into a network card of one of your PCs. This will be your test PC. No other equipment such as a router should be connected to the modem during the test.  

Reboot your test PC.

On your test PC please go to:

Network and Sharing Center (under Control Center)

Set up a new connection or network

Choose "connect to the Internet" and click "next"

Choose "broadband PPPoE"

Enter username and password provided by your Internet Service Provider (ISP) and click connect. This is not the same username and password which you use for your computer or Wi-Fi.  If you receive an error code refer to the DSL Error Codes below. Report the error code to your provider.  An error code 651 may indicate that your modem is not programmed in bridged mode. If this is the case the testing process in this article does not apply. 

If you receive no error after clicking on Connect then open a WEB browser such as Internet Explorer, Google Chrome, Firefox or any other WEB browser of your choice. Check if you can browse the Internet. If it works than your initial problem was with the equipment you disconnected for the test such as your router, network cables, etc. Your Internet provider will not be able to help you with your equipment unless they provided it to you.

DSL Error Codes 

Please note that the error codes below are specific to Microsoft Windows. This not  a complete list and it is operating system specific.  

600 An operation is pending. 

601 The port handle is invalid. 

602 The port is already open. 

603 Caller's buffer is too small. 

604 Wrong information specified. 

605 Cannot set port information. 

606 The port is not connected. 

607 The event is invalid. 

608 The device does not exist. 

609 The device type does not exist. 

610 The buffer is invalid. 

611 The route is not available. 

612 The route is not allocated. 

613 Invalid compression specified. 

614 Out of buffers. 

615 The port was not found. 

616 An asynchronous request is pending. 

617 The port or device is already disconnecting. 

618 The port is not open. 

619 The port is disconnected. 

620 There are no endpoints. 

621 Cannot open the phone book file. 

622 Cannot load the phone book file. 

623 Cannot find the phone book entry. 

624 Cannot write the phone book file. 

625 Invalid information found in the phone book. 

626 Cannot load a string. 

627 Cannot find key. 

628 The port was disconnected. 

629 The port was disconnected by the remote machine. 

630 The port was disconnected due to hardware failure. 

631 The port was disconnected by the user. 

632 The structure size is incorrect. 

633 The port is already in use or is not configured for Remote Access dialout. 

634 Cannot register your computer on the remote network. 

635 Unknown error. 

636 The wrong device is attached to the port. 

637 The string could not be converted. 

638 The request has timed out. 

639 No asynchronous net available. 

640 A NetBIOS error has occurred. 

641 The server cannot allocate NetBIOS resources needed to support the client. 

642 One of your NetBIOS names is already registered on the remote network. 

643 A network adapter at the server failed. 

644 You will not receive network message popups. 

645 Internal authentication error. 

646 The account is not permitted to log on at this time of day. 

647 The account is disabled. 

648 The password has expired. 

649 The account does not have Remote Access permission. 

650 The Remote Access server is not responding. 

651 Your modem (or other connecting device) has reported an error. 

652 Unrecognized response from the device. 

653 A macro required by the device was not found in the device .INF file section. 

654 A command or response in the device .INF file section refers to an undefined macro 

655 The macro was not found in the device .INF file section. 

656 The macro in the device .INF file section contains an undefined macro 

657 The device .INF file could not be opened. 

658 The device name in the device .INF or media .INI file is too long. 

659 The media .INI file refers to an unknown device name. 

660 The device .INF file contains no responses for the command. 

661 The device .INF file is missing a command. 

662 Attempted to set a macro not listed in device .INF file section. 

663 The media .INI file refers to an unknown device type. 

664 Cannot allocate memory. 

665 The port is not configured for Remote Access. 

666 Your modem (or other connecting device) is not functioning. 

667 Cannot read the media .INI file. 

668 The connection dropped. 

669 The usage parameter in the media .INI file is invalid. 

670 Cannot read the section name from the media .INI file. 

671 Cannot read the device type from the media .INI file. 

672 Cannot read the device name from the media .INI file. 

673 Cannot read the usage from the media .INI file. 

674 Cannot read the maximum connection BPS rate from the media .INI file. 

675 Cannot read the maximum carrier BPS rate from the media .INI file. 

676 The line is busy. 

677 A person answered instead of a modem. 

678 There is no answer. 

679 Cannot detect carrier. 

680 There is no dial tone. 

681 General error reported by device. 

682 ERROR WRITING SECTIONNAME 

683 ERROR WRITING DEVICETYPE 

684 ERROR WRITING DEVICENAME 

685 ERROR WRITING MAXCONNECTBPS 

686 ERROR WRITING MAXCARRIERBPS 

687 ERROR WRITING USAGE 

688 ERROR WRITING DEFAULTOFF 

689 ERROR READING DEFAULTOFF 

690 ERROR EMPTY INI FILE 

691 Access denied because username and/or password is invalid on the domain. 

692 Hardware failure in port or attached device. 

693 ERROR NOT BINARY MACRO 

694 ERROR DCB NOT FOUND 

695 ERROR STATE MACHINES NOT STARTED 

696 ERROR STATE MACHINES ALREADY STARTED 

697 ERROR PARTIAL RESPONSE LOOPING 

698 A response keyname in the device .INF file is not in the expected format. 

699 The device response caused buffer overflow. 

700 The expanded command in the device .INF file is too long. 

701 The device moved to a BPS rate not supported by the COM driver. 

702 Device response received when none expected. 

703 ERROR INTERACTIVE MODE 

704 ERROR BAD CALLBACK NUMBER 

705 ERROR INVALID AUTH STATE 

706 ERROR WRITING INITBPS 

707 X.25 diagnostic indication. 

708 The account has expired. 

709 Error changing password on domain. 

710 Serial overrun errors were detected while communicating with your modem. 

711 RasMan initialization failure. Check the event log. 

712 Biplex port is initializing. Wait a few seconds and redial. 

713 No active ISDN lines are available. 

714 Not enough ISDN channels are available to make the call. 

715 Too many errors occurred because of poor phone line quality. 

716 The Remote Access IP configuration is unusable. 

717 No IP addresses are available in the static pool of Remote Access IP addresses. 

718 PPP timeout. 

719 PPP terminated by remote machine. 

720 No PPP control protocols configured. 

721 Remote PPP peer is not responding. 

722 The PPP packet is invalid. 

723 The phone number, including prefix and suffix, is too long. 

724 The IPX protocol cannot dial-out on the port because the computer is an IPX router. 

725 The IPX protocol cannot dial-in on the port because the IPX router is not installed.. 

726 The IPX protocol cannot be used for dial-out on more than one port at a time. 

727 Cannot access TCPCFG.DLL. 

728 Cannot find an IP adapter bound to Remote Access. 

729 SLIP cannot be used unless the IP protocol is installed. 

730 Computer registration is not complete. 

731 The protocol is not configured. 

732 The PPP negotiation is not converging. 

733 The PPP control protocol for this network protocol is not available on the server. 

734 The PPP link control protocol terminated.. 

735 The requested address was rejected by the server.. 

736 The remote computer terminated the control protocol. 

737 Loopback detected.. 

738 The server did not assign an address. 

739 The remote server cannot use the Windows NT encrypted password. 

740 The TAPI devices configured for Remote Access failed to initialize or were not installed correctly. 

741 The local computer does not support encryption. 

742 The remote server does not support encryption. 

743 The remote server requires encryption. 

744 Cannot use the IPX net number assigned by the remote server. Check the event log. 

752 A syntax error was encountered while processing a script. 

769 The specific destination is not reachable.(Network Card may be off)