I have a desktop pc with inbuilt modem but when i go for bsnl broad band connection, problem arise.?

That is the bsnl employer told me that, inbuilt modem will not work, u have to purchase new modem, then what is the use of this inbuilt modem. and for further information i would like to tell u that i have seen the modem in the system hardware list of my pc. please reply me.