Reboot the machine, verify your Username and Password, and try again.
Check for realms, if in NT make sure you have nothing under domain, accept any auth including clear text is checked, and try unchecking Enable PPP LCP extensions.
Make sure logon to network isn't checked. Make sure that nothing is typed in the DOMAIN field if this is NT.
This is often a POP problem.
Try logging onto a different POP.
718 is usually on the ISP's end, but NOT ALWAYS.
Unless mutiple calls are being received by the technical support of your ISP then it will be down to your own computer.
Delete the pwl files (WARNING - make sure you know ALL the passwords for the computer).
Recreate dialer.
Full uninstall and reinstall of dialer, network, and DUN/RAS.
This can sometimes also be a communications problem caused by heavy line noise or modem problems.
Try updating the modem drivers, inits, commas, etc...and have a line noise test performed.
For more info on error 718 visit: Google Groups Error 718