Did you type everything sensitvely such as: spaces, lowercase letters, uppercase, dashes, etc?

How to: Fix the GUID bootloader (Blinking cursor)
There's an issue with the script that installs the GUID bootloader.

Easy to fix :

1 - Boot with the DVD.
2 - Press F8, then type "-s"
3- type "cd /usr/standalone/i386"
4 - type "dd if=./guid/boot1h of=/dev/rdiskXsY bs=512 count=1 (X is the disk number and Y is the partition number on which you installed Leo)
5 - type "dd if=./guid/boot0 of=/dev/diskX bs=400 count=1
6 - type "./startupfiletool -v /dev/diskXsY ./boot_v8"

GUID bootloader must be now installed correctly.

You should make sure.