so. I googled and wiki-ed far and wide and found no answer. But I fixed the problem myself and here I am to post it here just incase.
I'll keep it short and simple.
What happened was is I had this random box just sitting around doing nothing with no os on it. I put Debian 3.1 on it. After it went through the phases of installing and updating it's packages it rebooted itself. Up came the bootloader and loaded normally.
then after all the net config messages and other misc garbage that no one pays attention to anyway - it tried to load gdm.
Then came the blank screen with a white cursor up at the top, not blinking. No mouse,no input at all, and Alt-Ctrl-F 1-7 did nothing.
Apparently I had forgotten that there were two video cards. One Intel Onboard card and another ATI Radeon (some number) card in one of the AGP slots.
So what happened was when Debian configured xorg it put the Intel onboard autodetect instead of the ATI card. the Intel card was not hooked up through the monitor and disabled in the bios.
Plus - who would want to use onboard when they have a fairly new ATI card just sitting there collecting dust?
So I had to manually reboot the box, boot from the rescue mode option from the bootloader. log in as root (It auto does this on 3.1 and Ubuntu 5.04) then simply type:
dpkg-reconfigure -plow -xserver-xorg
then a nice little text based prompt follows and asks you awesome questions that you normally wouldn't know off hand, like the horizontal and vertial refresh rates of your monitor, etc...
and of course the things that matter: the XServer driver (ATI in this example) and the card identification and bus position.
This works equally for Debian and Ubuntu. Ubuntu just gives you the blank screen always, but Debian will sometimes load a generic driver 800x600 screen res with 24bit color scheme until you change the xf86Config which can only be changed under root, which cannot be logged into under the gdm.
So, maybe if someone has this problem in the future and they google, they'll find this nicely put answer. Or maybe it just gave me a chance to complain about my woes of yesterday.
Hm. So much for short and simple.