This may be a question of manual configuration of the new modem.
I have memories of frustration when installing in a new 98 system, there always seemed to be conflict between the sound card and the modem.
If you can find the place (in Control Panel) where you can choose the Com Port and the Interrupt, then you may find that you can choose Com3 Interrupt 5.
Look out too, for an opportunity to make your modem search for itself
That always seemed the place of happiness for me!