Moved HD with Tiger OS to new computer, but it won't boot.

[applemaz]

I had OSX Tiger on my main computer and decided to remove that drive and put it into an older Mac which is on the certified list to run Tiger.

After starting up I get the ? and Mac System folder. It worked fine when it was in my previous computer. What can I do to get the older Mac to boot off of this drive?

I don't want to reinstall the OS, I just want the older Mac to see the system folder on the HD and use it to boot.