When you see the following prompt with a blinking cursor instead of your RHEL 5 (Or CentOS/Scientific Linux v5 obviously) server booting, you will have in all likelihood have to re-install GRUB.
Step 1: Insert a copy of your RHEL DVD (or mount the ISO if this is a virtual machine) Make sure your machine is set to boot
from the DVD/CDROM drive
Step 2: When you get to the boot screen, type the following and press enter
You will have to answer a few basic questions. The last question will ask whether you want to mount as ‘read-only’. Be sure NOT to mount as ‘read-only’
Step 3: When prompt appears, change to real root (‘/’) on your hard disk
Step 4: Run the following command to re-install grub
# Replace 'sda' with the device name of the drive you want to boot from. For IDE based disks, this will probably be 'hda', etc. grub-install /dev/sda
Step 5: Type ‘exit’ twice and reboot the machine. Remember to remove any removable media.
You should now be able to boot into your (non)broken system again.
Thank you very much, you just made my day 🙂