|What shows in Device Manager when you click the "+" sign?|
If the Modem is never Found on reboot how do you know what to install manually? What method are you using to manually install?
If this is a PCI Modem, you'll need to get someone to physically remove the Modem Card from the PCI Slot and reboot without the modem.
Next, shutdown, Re-install the Modem in the first PCI slot and reboot.
If Windows refuses to automatically detect the Modem, you may have a bad Modem.
There may be some better info at this link.
There is nothing to learn from someone who already agrees with you.