First, i like to know if ur modem is an external modem or internal PCI modem.
If you are using an external modem, it could be the physical wiring issue that did not allow the computer to recognise the presence of the modem. otherwise, it could be you didnt set up ur dialing location. Or your modem drivers were not installed or not recognised by the OS.
Then, if you are running an internal PCI modem, overclocking may cause the issue. I had personally come across issues like that before, coz the so call overclocking that Mobo offers are actually increasing the FSB thing and that affects the PCI interface. *My SB PCI Live card refuse to work!*
Second, i like to query abt ur hardware setup. You are using a 800Mhz FSB PC yet, you did not use Dual Channel Memory... Why not? Coz if you are not using DC memory chips, the 800mhz wont be optimized. Its like a 533Mhz FSB using a 266Mhz DDR Ram.. bottlenecks my friend.
PIV 2.6Ghz w HT 512k Cache 800Mhz FSB
GA 8IPE1000 PRO
Twinmos 1GB DC 400 CL2.5
120GB IBM 7200RPM w 2MB cache
120GB Maxtor 7200RPM w 8MB cache
Nvidia FX5200 128MB
Philips SXGA 150S4 15\" LCD
Cooler Mastor Centurion
Global WIN Cooling System
TDK Cyclone 48X24X28X CDRW
Intel PRO 10/100 TX
Sigma IrDA Port
PixelView FM/TV Pro