Reboot
Shut down the computer, wait 60 seconds, reboot and try to connect again.
Modem correctly plugged in?
Make sure that the modem cable is plugged into "Telco" or "Line In/Line" vs. "Phone" on the computer.
Cables/Splitters/Devices
Be sure modem cable is plugged into correct jack on the computer and that it is seated securely at both ends. Ideally, cables should not exceed a length of 6 feet. Unplug the cable from the modem and jack and reseat; try another cable (from phone). Remove any line splitters, surge protectors, fax machines, duplex jacks between the modem and wall jack and try to connect again. Also try unplugging phones (even those on a second phone line as there may be a problem with internal wiring) and other devices that may be causing interference. Be sure the line is not in use. Test the cable and jack used by the modem by plugging in a phone.
Electrical Interference
The phone cord should not be wrapped around or routed close to any cord carrying electrical current and should be kept at least 3" from electrical lines and devices.
Do you have voicemail?
There may be messages waiting. Voicemail causes a beep to occur when the line is picked up so the modem doesn't hear the dialtone right away. If this is the case, a "stuttering" tone is generally heard. Clear your messages before trying to connect.
Is the correct modem selected in connectoid?
Go to Network Connections (Dial-Up Networking) and be sure the modem selected for the connection is correct.
Software 'stealing' connection
Check to be sure that other software installed on the computer is not attempting to dial and using the modem com port. Some fax software will monitor the modem and make it appear the modem is in use by this program.
Dialing properties and access number
Check dialing properties. Do you have Call Waiting? Is the phone number correct?
Check login
Is your username spelled correctly and in lowercase letters? Be sure the CAPS lock key is NOT on and, if there are numbers in your username or password, be sure the NUM lock key is on. For further troubleshooting, see Troubleshooting: Username & Password.
Old connections?
Check your Network Connections (Dial-up Networking) folder for old, unused connections. If any exist, delete them.
Delete/Recreate connection
Go to your Network Connections (Dial-up Networking) folder. Make a note of your username and access number, then delete the connection (right-click on the icon, then click Delete). Create a new dial-up connection.
Winsock/wsock32
You may need to extract a copy of the winsock.dll or wsock32.dll files as they sometimes become corrupted or you may need to remove Winsock 2. You can extract these files by using the System File Checker/System Configuration Utility in Windows 98 and up. NOTE: You must first locate your operating system CD or ensure that you have the appropriate Windows .cab files on your hard drive before performing any file extraction.
Modem drivers or init string
Re-install modem drivers and check for modem driver updates or firmware on your computer or modem vendor's website. A modem initialization string may help if you have problems connecting or staying connected. If you have a v.92 modem, try disabling v.92 with an init string. Check your modem's documentation or modem manufacturer's website for this information.
Personal firewall or WinXP firewall
Disable firewalls, including McAfee, Norton, etc., and if Windows XP, be sure the firewall option is not selected.