Make sure that your BIOS is NOT configured to set up PnP devices, Windows will handle the PnP setup. Some internal modems are Winmodems, they off load some functions to the computer CPU that are normally handled by onboard processors on a traditional modem. This obviously uses some of the computational power otherwise available to run applications. Manufacturers are not always up front in identifying winmodems, so look for the fine print on the box. There are differing setup requirements for modems so the best advise is to carefully read the installation instructions that come with the modem.
Internal modems cause the most confusion and aggravation so let's look at some considerations.
If you use a Serial mouse, it is normally installed on Com1, you could disable Com2 in your BIOS and use Com2 for your modem, but that is throwing away a port that you could use for other purposes, you would use Com2 for an external modem. If you have a mouse on Com1, do not use Com3 for the modem. Com1 normally shares the same IRQ as Com3. Com2 shares an IRQ with Com4. Of course, you only have 15 IRQ's in total and most will be needed for other devices.