I've a super socket 7 motherboard (P5V? I can't recall the brand and it's not labeled on the MB) equipped with a K6-2 300mhz cpu, 256mb ram, and running Windows 98SE.
I've been using it with an Nvidia GeForce MX200 AGP video card (32mb ram)

I decided I wanted to upgrade to an FX-5500 video card. I had forgotten that this motherboard was actually AGP, and got a PCI NVIDIA Fx-5500. Then I found an inexpensive AGP FX-5500.

Now, the machine boots with the MX200, though I have to sometimes hit the reset button a couple times before it boots.
The machine also boots with a PCI Trident card (I don't think it has 3D acceleration) with 4mb ram. And I don't have to hit the reset switch.

I tried the FX-5500 PCI... both FX-5500s have 256mb ram, btw... and it wouldn't boot. I tried the FX-5500 AGP... still wouldn't boot. Nothing. doesn't even bump the floppy as it normally would.

I tried making some adjustments to the bios (such as making the AGP aperture 256mb), but it's done no good.
It's possible, I suppose, that I got 2 bad video cards in a row, but seems much more likely either an AGP issue or a bios settings issue.

I wanted the FX5500s because I want to install the DirectX 9 SDK on the system.

What I ultimately am trying for is a 300mhz system with 256mb ram and a 3D video card compatible with DirectX 9, and running Windows 98SE.
This similar to what I ran in the late 1990s early 2000s, iirc (in fact, this machine was my main machine back in the day).

Can anyone offer any suggestions as to what I can do to troubleshoot this issue?

I don't know if it's related or not, but even though the system is plugged into power from the wall, the CMOS battery *sometimes* seems to forget *some* of the settings. Most notably, the time. Last time I used the machine was the afternoon of May 31st, and when I fired it up tonight at 21:20 on June 4th (using the Trident card), the bios said the time was 14:23 on May 31st.