right another system problem!

I Have a:

Duron 700
J663AS MB
Ge-force 2 MX
128MB Ram
Diamond Supra 56K Modem

All new hardware (All ours except Modem) What happens is when the system is on and someone calls the phone line then the computer just HALTS, and windows seems to run as if a 14Mhz CPU, example is when you click start button it takes about 5 minutes to pop up. The PC runs fine until some one rings the line! This happens all the time.

So, we removed the modem and tried it in another system, this system worked fine so the problem seems to be in our MB?? so we installed one of our software modems and there was no problem. So we come to the conclusion of incompatibility, right? wrong, The customer had this config working before with no problems didnt change os or installed any other software, so we are now stuck! AGAIN, goddammit!

Any help from my fellow technicians would be much appreciated,, again!

Thx <IMG SRC="smilies/eek.gif" border="0">