It's definitely NOT the PSU (unless it's below 200W), it's not a molex/floppy connected card, it'll run of the juice on the AGP bus, and likely draws the same/less than a GF4.
From what I've seen so far (arrived late) I'd say you need to a: uninstall every trace of the voodoo drivers (both cards should run without drivers in a basic low res. mode) and try again.
IF that doesn't work, b: Before doing anything else, check the info boards at your mobo manufacturer's site, and even the ATI infosource. See if they have seen this before. Also take a look at your bios settings and see if anything is out of whack to you.
Then first get the most recent MOBO-AGP drivers, second install the motherboard AGP drivers (again!), then power down and restart with the new AGP drivers (make sure Windows didn't re-install something, if so un-install the vodoo drivers again) Then power down and swap cards. Now see what happens (and pray, which is S.tandard O.perting P.rocedure for fixing computers). IF that doesn't do it, I don't know what to tell ya.
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