Had this problem myself with a G200, the culprit was Bus-Mastering and not having an IRQ assigned. Disable Bus-Mastering then make sure you have an IRQ assigned to the card and that it isn't conflicting. You may have to swop a few cards around in different slots to do this. Then re-enable bus mastering and things should be ok.
If it isn't that then I don't know,
If it isn't that then I don't know,
Comment