Snow Leopard installed onto external hard drive won't boot

[PJ_Mac]

Hey all,

Using the guide found at http://lifehacker.com/5360150/install-snow...acking-required I managed to successfully install os x to my external hard drive. After the successful installation it told me to restart. So I restarted into the hard drive I installed the OS on, and I never get the loading screen. All I see is a white underscore on a black background, except for when I boot on my MacBook. Then it works perfectly. What did I do wrong?

 

–During the installation, it required that the hard drive be GUID Partition Table. Is that what it's supposed to be?

 

THANKS!