"loaded the pkg disc, including all the 2.6 modules etc,"
may be second disk
"i did xorgconfig like i have a million times.""
BEFORE DOING THIS GO THROUGH ALL THE OTHER SUGGECTIONS
i think frame buffer is causing the problem
this is my guess..
earlier u didnt loaded the module of ur card(say nvidia), so it took vesa and booted. now when u installed the modules for 2.6 ur module is loaded (provided with slack)and it seems the module may not be compatible (or a clash with incompatible modules loaded-like rivafb and nvidia will clash)
if so u try booting with 1st cd at the boot prompt
boot: bare.i root=/dev/hdax noinitrd ro
bare.i or the kernel u use to boot and
root=/dev/hdax ur / partition /
1. edit lilo to standard vga,
2. run lilo
if u can boot, no problem
then install the driver for ur corresponding display driver(nvdia). installer wil make module for u