Here's an example of what can happen when you plug a plain FW400 cable (with nothing connected) into a FW card while the PC is on...
I guess the name's well deserved, there was quite a flash. The FW card still worked with a FF400 in another FW port (even using the FF as a hub for video transfer), but no longer provided bus power.
In spite of the slight damage to the PCI slot's plastic housing, the replacement FW card works fine. Good thing it was a PCI card and not onboard FW, else I might have had to buy a new mainboard. ed:
The ribbon cable goes to a MIDI/Game connector, haven't tested it, but I never use it anyway.

[Update 2020: The mainboard worked for another 10 years of increasingly irregular use, and finally seems to have given up some time last year. Not sure if related to the FW burnout]

Regards,
Daniel Fuchs
RME