Other than the fact that you have two modems, you haven't given enough information to receive much help. An output of lspci would be useful. What kind of modems do you have?
There is one thing that you can try. If your modems are on PCI cards, turn off PnP OS in the bios. Having this on, will disable shared IRQs. This purpose for this option is to allow running old 16 bit MSDOS drivers.
Here is a web site that explains this: