One last thing before you give up.
Do you have a driver for this modem? If so it has to be the proper one.
Do this one more time.
Remove the modem from device manager.
And while your there remove com1 and com2 also.
Shutdown.
Remove the modem again.
Boot up.
Go into the bios and disabling com1 and com2?
Save and reboot.
Check device manager to make sure removed items are not there.
If all is good reboot and enter the bios.
Disable the sound in the bios, Look thru all of the pages very carefully to make sure you disable all instances.
Save and reboot into safe mode again.
Go to device manager and remove all items related to the soundcard.
Shut down.
Install the modem and boot up.
If the system wants the driver insert the CD or Floppy with the driver on it.
We will try to get the modem working first then deal with the sound........
