are you by any chance using a geforce3 card? try:

echo hwaccel off > /dev/vgactl

and see if it works..

even though the video colors are all wrong you should still be able to
open a new rio window, or type the command in the ones already open.

or you can log in in as 'none'; do a 'disk/kfscmd allow'; edit
/usr/glenda/lib/profile and add the above command before the 'exec
rio' line

when logged in as 'none', ed is the standard editor.