P5F76, Pentium-S 133, 32MB SDRAM

I was going through, testing boards today and came across something that caused me to scratch my head. I'm sure there is a simple explanation. I just dont know what it is and I'm hoping someone here does.

My go-to video card for testing and workbench things is a Trident 9680. I couldn't tell you why I chose that particular card, but I did. The 9680 works fine for the most part. I've never seen it not behave properly. Today I popped it in the aforementioned P5F76 and the system wouldn't post. I moved it around trying different PCI slots but noting. I thought the board was dead. On a hunch I slapped in an ISA vid card and the board posted right up. I tried a Cirrus Logic 5434 PCI and the P5F76 posted right up on that as well. Tried the 9680 again and no joy.

So, what keeps the board from booting when the 9680 is in? I guess my test bench card is going to be a CL 5434 from now on, but it would be nice to know what the stopper here was.