My IVM doesn't work with my PBX line

[karmarule]

dudes... pleassseeee help me! PLEAAAAAASE! if some one knows this

I have an old external Acorp fax,voice,data modem which is connected to our pbx lines, and I have IVM 4.02 installed on my computer, configured for testing. when someones calling, it doesn't even ring!!! no logs, no ring,... nothing! but actually when I connect it to daily used lines (not my pbxs) it answers calls, it has logs, it rings and so on... I thought it would be the modem problem but I actually installed Fax Talk Messenger 7.0 pro on my computer, tested with pbxs lines, it worked fine, it could answer calls. this might show that the modem is ok and theres nothing wrong with it. but how come IVM doesn't even ring with PBX lines? PLEASSSSSSEEE if some one knows this, HELP ME!!!