sounds to me you need to reconfigure X, it seems as if you setup your box to boot up into runlevel 5, you need to change this to runlevel 3 in your inittab file. once your then at the command prompt, try running Xconfigurator to get X working, any problems in doing so .... check out www.xfree86.org
for info on your video and monitor and checking if its compatible or not. If you don't know how to change your runlevel.. at the lilo prompt, type linux 3 or if you boot up, you can switch terminals to get to a login prompt with ctrl-alt-F1 thru F6, or can ctrl-alt-backspace to kill the X windows session.
your modem sounds like it needs to be reconfigured too.. what kind of modem is it? is a winmodem.... ? goto www.linmodems.org
to find out if yours is or not.... and if its not then try reading the howto's on modems at www.linuxdoc.org
to get you started.