booting from an external

Okay guys helps me out pleeease... Alright so I have an external hard drive and I was booting an os from there fine for about a week. Then I tried installing Tiger to this external drive, (in a different partition), but it won't boot up from it. I have gone to system pre> startup disk and selected it, but when I hit restart it shows this really small picture that looks like a finder then it just restarts from my internal hd. When I hold down option at startup it only shows my internal drive. Help me please!

 

well its a g-drive q. I'm using a firewire 800. It worked great with the first operating system that I was booting from. That os is still in beta form btw. Anyway the other day I tried to put tiger on a different partition and since then it doesn't work. I can see the drives from the start up disk, but when I select them and hit restart it shows a finder with a question mark, and only boots up my internal.

 

Oh okay. I had Leopard running from one partition and it was working fine. Then the other day I tried to put tiger on another partition and since then neither has worked. I see each os when I go to sys pre> startup disk, but when I select any one it just shows a finder picture and then a question mark at start up. Then it just boots up from my internal drive. Sorry about not being specific. If there's anything else just ask. I just want to get this to work again.

oh I have a powerbook G4 1.67 Ghz.

 

does anyone know anything about this?