Yes, as philcom says the Error 678 can occur if:
- You are dialing the wrong number
- There is a problem at your ISP or in the telephone line/network
- Your modem is unable to handshake with remote modem before allotted time.
Since you already tried everything at your end, try using some other modem/card or call your ISP.
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Error 721: The remote computer is not responding.
Error 678: The remote computer failed to respond.
Error 691: Access was denied because the user name and/or password was invalid on the domain.
Error 777: The connection attempt failed because the modem or other connecting device on the remote computer is out of order.
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All the best.