These PCI modems can be a bit of a pain:
Deleting the modem from your Device Manager can work, but first you need to get it installed.
Try deleting all the software and removing the modem. Then reboot. Then switch off. Now coems the important part. Check the manual to see whether you install the software or hardware first and make sure you get it in the right order.
When you install the hardware, put it into a differnt slot to the one it was in.
When you install the software. make sure you reboot BEFORE trying to use it.
If you are still experiencing difficulties, it will be down to a problem in Windows itself. You might get away with reinstalling over the top but you may have to reinstall Windows (back up all your data first). In either event, take out the Modem before you start so that you can control its installation when you get back controil of the PC after the installation of Windows.