FireWire isn't working?

What are the specs of the other computer?

If the other computer does not support the connection to your iBook, you could

still test the FW400 port in the iBook by use of an external FW enclosed HDD.

Usually the hardware of your own machine would appear in System Profiler, yet

may not if there is a hardware issue or one of other cause. You could try & see

if the the problem appears limited to your iBook, if a Power Management reset

could allow the computer ports (FW especially) to re-appear. Did you try this 2x?

Depending on the model and vintage a PMU reset may vary, among instruction here:

•Resetting PowerBook and iBook Power Management Unit (PMU) - Apple Support

Since the computer (iBook) is beyond the scope of a retail Apple Store, you may

need to discuss its status if you cannot restore use of essential ports, with another

service specialist at an independent Apple authorized service provider, one with a

preference and skilled staff with experience with older hardware configurations.

In some regions or countries, the options to have older gear serviced vary from fair

to non-existent. In the US and some others, specialists will accept shipped portable

computers for repair, restoration, and can perform intense diagnostics. For older

gear, wegenermedia is one of the better examples I'm aware of...

Good luck & happy computing! 🙂