I'm wondering if what YBR means by 'IDE cable' is in fact a ribbon cable connecting the sound card to the breakout box, and that it works OK when the breakout is disconnected, but fails when hooked up.
It would help if I had a better idea of what 'not working' meant - as in whether the sound card fails to work or the computer stops working entirely. If the latter is the case, power could be an issue.
Of course, if you have a friend with a high-spec (with a hefty PSU) PC handy, you could always try the card out in their machine and see what happens.
What sound card are we talking about here, and what's your machine's spec and config?
J.