Do this:

Bootoption at startup:

linux 3 vga=791

Login as "root"

pico /boot/grub/menu.lst

Change the value of vga= in the following line like this:

title linux
kernel (hd0,0)/vmlinuz root=/dev/hda3 vga=791
initrd (hd0,0)/initrd

After this CTRL + O and CTRL +X to exit.

Activate the fbdev with:

sax2 -m 0=fbdev

and configure your resolution and Frequency (60Hz recommended) Exit sax and activate GUI with:

init 5

Test it, post result.