unable to boot from external drive...


i have a fantom 160 gb external firewire drive that ive used for the past year or so to backup and store music on (since my pb's drive is small).
i bought my pb used a few years ago and didnt get system disks, so i have subsequently used my school's open licensed tiger discs to upgrade (whether this is actually appropriate or not im not sure - but thyats not the issue).
since i dont have my own discs, ive never been able to repair my hard drive via disk utility. lately, ive felt it would be a good thing to do, since things (including startup) have been a little off.
so i used carboncopycloner to clone the disk to my external drive, expecting to be able to boot from that drive and do any necessary repairs on the internal one. now, though, if i use the fantom drive as the startup disk, i initially get the grey screen with apple, then the spinning lines - but it stops there. my powerbook shuts itself down. no kernal panic. nothing. just stops.
once i turn off/disconnect the external drive, it boots up fine from the internal drive (however, it usually takes a regular restart and then a hard restart - from the button on the back of the machine - to get it up and running. the first restart will get the machine running, but wont turn the screen on).

any ideas?