It looks like I bricked my Kayak XU800 board. BIOS crisis recovery doesn't work either. There is no floppy activity. The BIOS chip is not socketed unfortunately, and I don't want to place an empty socket on the board with the risk of ruining the whole thing. So I figured I could hook up an empty socket in mirror-image. Test drive using a spare EEPROM:

Only a few pins left who are making bad or no contact... I slightly bent the contact points in the socket using a modified staple.

Sometimes you need to cut the bottom out for sockets to seat deep enough to make contact when on top of a chip.

BitWrangler wrote on Today, 19:35:

Sometimes you need to cut the bottom out for sockets to seat deep enough to make contact when on top of a chip.

I see what you mean, but here's our brick:

Not many tall components, just a few low profile SMD caps or resistors but these are not obstructing.

I had mixed luck flashing chips while still in system, stuff like whole mobo trying to power off injected voltage etc, sometimes powering on and keeping it in reset helps

Well, I did something pretty dumb and impulse-bought a GPU for my retro PC, even though someone already offered to give me the same model I was looking for without paying £50 for it.
(I may be stupid)

Installing the 7600 GS has given my retro PC a good boost and saved the 5700LE for if I want to make a Pentium 3 PC with it one day, though I think I'm also running into some driver issues. (I just chose the most up-to-date drivers, which I know is not a good choice so I'll be looking into some better ones soonish)
Sonic Heroes (running at 640x480) does run better, but also noticeably runs way worse than I'd expect for a game that needs 16mb of VRAM and a Pentium 1, with more the rising platform gimmick elements in the first level causing a whole lot of lag.
Spore runs better but running in fullscreen constantly forces me out of it, and Peggle's hardware acceleration actually works better than software mode but the game looks like it was stretched slightly with nearest-neighbour filtering.
I've not yet tried any other games, although Discord Messanger does still work and Mypal does too and slightly better (but not by much)

There's definitely some kind of bottleneck in this computer, though I'm not actually 100% sure if it is drivers or if it's the CPU (3.06ghz Pentium 4 HT), or the motherboard (SiS chipset + no actual microcode for hyperthreading), or the USB 3.0 PCI card is saturating the PCI bus, or maybe Windows Vista is just too much for this thing after all and I should cut my losses & give up on it.
(or maybe I accidentally didn't put the molex connector in properly and it's throttling performance. I did try to put it in as far as I could but I didn't want to risk damaging the GPU board...)

(At the very least, I think hardware-wise this system is basically maxed out now for what the motherboard can feasibly support. there's definitely room to improve if I get a better motherboard, but I think that'd ruin the charm given how that's the only thing left in the build from the original computer.)