G4 Dual Optical firewire card replacement?

I have a Power Mac G4 Dual Optical tower with firewire 400 ports that don't work anymore. They've been on the fritz and now don't work at all. The two usb ports still work but can't power anything like my ipod, or a usb hub, or any usb device that doesn't have its own power supply. I would like to replace them (the whole card...) but don't know anything about how they are connected inside my computer. Are they part of the mother board? I can't actually see that part of my computer as there is some parts in the way.
I was looking into a Sonnet Tango Firewire and USB card that requires an expansion card but it has a warning that it won't provide the same amount of electrical power as a built in one. But can I replace my built in one? Is this possible? How can I do this?

Have a look at these suggestions on zapping the PRAm and NVRAm from Apple Discussions. Do the ports show up on the System profiler? Sometimes a fresh install of the OS helps:-

http://discussions.apple.com/thread.jspa?threadID=1626008&tstart=0

So then someone said "here's the obscure incantation that will fix your persistant woes..."

Thanks you.

LOL got it going again?