Switching Startup Disk-Getting Kernel Panic message

I own a PowerBook G4 laptop. My LCD screen is broken (I use a monitor). Since the monitor doesn't display correctly when I go to the install menu, I recently upgraded to Snow Leopard from Tiger by installing it onto my clean partitioned external hard drive (using disk utility) via a different power book.

I initially had no problem switching my startup disk to my external so I could run snow leopard on my machine. However, once I switched the startup disk back to tiger, I haven't been able to change my startup disk back to the external without getting a kernel panic message, which looks like this:

http://www.ourhangout.net/archives/Kernel_Panic-1p0f.png

Does anyone have any idea what I can do to A: resolve the problem so I can switch my startup disk and B: ensure that this doesn't happen again.

Thank you!

First off, we need to be clear on what you are doing. Snow Leopard will not run on a PPC Mac. It is Intel only.

Thanks for the reply. I'm on an Intel machine. I was able to run snow leopard on it temporarily so the hardware is compatible.

In that case it would not be a Powerbook, a G4 or a G5 as those are all PPC machines.

If this copy of Snow Leopard was installed on a different Mac, it just may be that it does not have the correct drivers installed to boot your Mac. In a case like that it may run one time and not the next.