I misunderstood---I thought you were not able to boot into your OS.
Here's a clue (from my RedHat EL4 setup):
The grub directory includes a file named splash.xpm.gz
In the menu.lst file are the following two lines:
if I hide the splash file, then I get behavior similar to yours. My hunch is that --without an image file--"hiddenmenu" causes nothing to be displayed.
Try some experiments--or read the GRUB manual (or both...