Video Card Issues(?)

Alright, so I'm pretty puzzled by this one.

All of my games play as though I'm using software acceleration.

Right now I'm running with Windows XP Professional, an Athlon XP 2800+, 1 gig of RAM, and a Geforce 5200 FX, yet I can't even run a game that's got a Geforce 4 MX as part of a Recommended setup without massive slowdown (and that's at the lowest settings). As I said in my earlier thread, I don't have any overclocking going on, and from it looks like everything is set up properly in my BIOS.

I've installed new video card drivers (nVidia's official ones as well as some Omega drivers whose version number seemed horribly out of date but managed to run a little better than the nVidia ones. I've also updated DirectX (was at 9.0c already but I figured it couldn't hurt).

Does anyone have a clue what could be going on? Windows functions perfectly fine, the directx demos for 7, 8, and 9 all work properly, and even when I load games the initial animations look perfectly fine (though I don't know if they're prerendered or not). I can play videos without problems, and this is pretty much the only thing that's wonky about my computer right now.

Jam it back in, in the dark.

I just reseated the card last week when I dusted the whole computer, actually. Cleaned out it's fan as well as the heatsink/fan on my processor to try and help cool things down a little bit. I know Fastwrite is enabled, and I imagine the second one is too since there were two AGP options in my BIOS and I have both of them on (as they've always been).

I'll try playing with the sides of my case off to see if heat's a problem, but I doubt it since it's a fairly old card and I don't think it even gets that hot.

Oh, and no BSODs, though every now and then the nvidia desktop manager will randomly have issues on me. I figure the recent driver reinstalls/upgrades I've done should take care of that.

There's nowhere I can't reach.

I accidentally opened up SiSoft Sandra earlier today and figured, what the hell, I'll check it's video card properties. It said that Fast-Writes is Disabled (something I know is enabled) as well as Isochronous Mode as not be enabled. No clue what the second one is, but the first puzzled me a bit, so I went into my BIOS and disabled fast writes. There was a bit of a performance boost, though it still doesn't feel like it's up to where it should be.

Later today I'm going to try enabling it again to see if it goes back to being poor performance or if it stays about where it is now.

This thing is sticky, and I don't like it. I don't appreciate it.