Try it in another slot, or try another adapter in that slot to see if the slot is damaged.

If the modem works in other mainboards and not on this mainboard, should tell you that there is a problem with the slot you are using...

now I don't know if it is a PCI (only one slot on the mainboard) or PCIe (three slots 2 1x and 1 16x) or even an AMR modem (no slot on mainboard for that interface), since you left out that information...

suggestion - as mentioned try other compatible cards to see if the slot(s) you are using are even functioning correctly...

use an USB Modem if you really need a modem instead...
 

Ben
"If it works don't fix it! If it doesn't use a sledgehammer..."
How to ask a question, when posting them to a professional forum.
Only ask questions with yes/no answers if you want "yes" or "no"

It sounds more to me that it's just a compatibility issue between the motherboard and the modem.  Have you tried other PCI devices at all in the same slots on the same motherboard to make sure it's not the slots?

I can't help but think it's a compatibility issue as I've seen the EXACT same thing with USB PCI cards.  Not all of them, but a couple.  And I've verified it between multiple USB cards, multiple motherboards, etc.  Some USB PCI cards, you could plug into seemingly any motherboard, and the computer wouldn't boot... or it'd freeze up, or go to a blue screen, different things sometimes totally random behaviors.  Removing that PCI card, and replacing with another worked 100% fine.

If you can still find a PCI card dial-up modem, they've been really cheap over the past several years.  Definitely worth just getting another to try.  You could even get one at a local store, try it out and return it most likely if it didn't work.  Then again, depending upon how far that store is, it might be cheaper just to toss it if it doesn't work.
 

THere is only one PCI slot on the motherboard. One of the sites suggested to install the driver first that allocates the com port and try installing the modem. I did that, i installed the driver and plugged in modem on only pci slot and rebooted the system and it boot up just fine but under device manager the modem is marked with yellow exclamation saying there is no driver installed for this device. it says controlles modem port and i tried to install the driver it say the inf file is written for win 95, i am tried win xp but it wont install. the same modem and driver worked on other desktop just fine. now i am looking into any resource conflicts and try to fix it but i am lost. any suggestions would be of great help.