help! Problem proceeding to windowsxp

when booting, the screen where youre to chose from safe mode, safe mode with networking, last good configuration appears and if i choose any one of those the computer suddenly hangs, i also tried to use the recovery console from the windows cd but when it tries to load the windows files something like that, the computer suddenly restarts and back to that process again. it happened after i’ve attached my old modem and i think the modem is already faulty. thanks