Modem does not work in Win 2K server

I reformated my Server and have the Active Directory set back, the modem I used to dialup through Win2K server does not work this time. I am using Aztech external modem, I tried with another same model modem, it still gave me the same error “Error 797: The connection failed because the modem (or other connecting device) was not found. Please make sure that the modem or other connecting device is installed.” I tried to query the modem, it gave me a result. I just couldn’t connect to the net. What might be the problem?