Dimension 4600 / Axel3d GeForce 7950 GT 512MB AGP: incompatable?

Problem: Upgrading from NVidia GeForce 5200 (256mb AGP) to Axel3d GeForce 7950 GT (512mb AGP) getting *no signal* on monitor at all. Upgraded to 650w PSU just for this card. I have tried MANY things. No change.

-old card still works and has same voltage registers (notches) in card as the new card

-new card *does* work in an older 'KMD Ultra' machine that has a 4x AGP slot.

-yes, I attached the required molex connector to the graphics card

-Bios (A12) and chipset are up to date

-tried all manner of removing/ pre-installing graphics drivers. Not convinced this is even an effective route, as drivers shouldn't matter prior to system post. Regardless, no effect.

-This mobo (02Y832) does not have onboard graphics, but have tried setting bios: graphics adapter to both/ either auto or agp, no effect

-fan on card does power

-RMA'd (returned) original card to vendor, got replacement, no change

-some other (old, as is my system and the card) forums have said this could be a dell bios issue? Does anyone have links to an alternate bios for this system I could try?

Running Win XP SP3, 1.25GB ram, 2.4 GHz Intel P4 (Dell Dimension 4600)

Links:

the problem card: http://www.amazon.com/Axle3D-Nvidia-GeForce-256-Bit-S-Video/dp/B002Q62VYO/ref=wl_it_dp_o?ie=UTF8&coliid=I38UJTQPO4LSF7&colid=GWV4I02NP2GM

the more than adequate power supply upgrade: http://www.newegg.com/Product/Product.aspx?Item=N82E16817339024&cm_re=650-_-17-339-024-_-Product