Server won't boot up ... no GRUB menu

I dont know what the heck happen but one of our DBAs was working on a cluster for oracle. Rebooted the box and viola, the OS won't load. After the POST message, I get a blinking cursor on the upper left hand corner. Doesn't even say "GRUB" or anything, it just blinks.

I tried going into rescue mode and re-installing GRUB but that didnt help. We even broke down the array just to check and that didn't help. I'm out of ideas. The data appears to be intact since I was able to chroot into the image when I boot off the CD. Any ideas?

RHEL AS 4.7

Sounds like the boot disk has not spun up to speed by the time the bios wants to access it. Some modern motherboards have a bios setting which introduces a delay to allow time for the disk to spin up. In your case, if nothing else has changed, the disk may be starting to fail.