I guess the first question here, is when the system comes up do you see the post messages. IE, BIOS info and Memory count? I am taking it you do and once Lilo or Grub starts you loose the screen. Knowing this is RedHat 9, I would tend to belive you are using X by default, meaning that you are booting into the graphical mode and not text. There are probably some differences between your friends monitor and the one you have, IE refresh rate and so on.
Here are some things to try.
When the system comes up, make sure you can see something on the screen first before Linux even starts. If you cannot it sounds more like a hardware/ Cable issue/ Graphics card issue.
After the post messages, at the prompt, try "linux text"
Another option is to wait until the box has booted, watch the HD light wait for it to stop, give it some time to finish booting, chances are it is doing fine. Wait like 5 min or so. Then, press Control+ALT+F2
This will take you to a virtual terminal, you can use F1 through F6 I just chose 2 as an example.
What this will do is take you to a text console where you can login. Once you have logged in I suggest taking the system back to text mode, which should be run level 3. You can do this as root by typing init3.
Once you have done that, I would re-run the Xwindows Configuration so that your monintor and adaptor are setup correctly.
Chances are when you loaded Redhat using your friends monitor it has a different refresh rate, and the monitor is going into guarded mode.
Hope that helps.
