I just purchased G 5. None of my FW 400 drives show up. Does anyone have a clue. All my music and video files are on those drives. If they don't show up the g 5 is useless. They are fine on my other Macs.

From the back of my head, in no special order…

Which G5 is it?
What's the origin of the FW 400 enclosures?
How are you connecting them?

If the enclosures are old (about 12-18 or more) you may have to upgrade their firmware. Check the manufacturer website.

If you try to use the front FW port of G5 desktop, try with the one behind the G5… The front one is… special. It works perfect for me, but it fried/disappeared/whatever for some others.

Have you tried to use a different cable?

Do the drives come from an OS 9 environment? If so, DON'T try to move them around between 9 and X. We'll see.

In the Apple System Information, do they appear? (apple menu/about this mac/more info) If so, do they appear in the Disk Utility?