There's not much else it can be to my mind, you've tried a new card, now assuming the card isn't DOA the only thing it could realistically be would be the AGP slot and there is not another easy way to verify this as you have tried a new card already.
To remove the chance the new card was DOA can you test it (and your original card) in another pc?
If they both or the new one run in a different pc then I would suggest that the AGP slot has gone and if your original card still fails to work it may be a casualty from the failed slot.
Sorry, but there's not much else I can think of to help you out.