did you try adding

STACKS=64,512
FILES=60
BUFFERS=40

or similar to config.sys

windows may not worry about it, but DOS does

beyond that it may be a driver or interrupt conflict, it might even be the mb and components being used; I'd imagine various incompatibilities creeping in as newer components leave backward compatibility behind

Hi gerry thanks for your reply, I will definitely try that and report back. I should point out that DOS works perfectly stable on this hardware, It's only when it tries to boot Win98 that it crashes complaining of a stack overflow.. To avoid ambiguity I'll just say that the error appears in DOS, ie not a blue screen general protection fault, but it pertains wholly to Windows. The full error is something like:

"Windows Protection Fault - Windows has been shut down to prevent instability caused by a stack overflow. Edit STACKS in config.sys to ensure stacks are properly configured." [massively paraphrased 🤣]

As far as I know based on my [probably poor] research all the hardware I'm using has official Windows 98 SE support [even the pci-e card has drivers!] I don't know about the motherboard though.. I tore it out of a prebuilt HP machine circa 2006/07 [??] which came loaded with XP. I was just excited to see it was LGA775 and would support the P4 I'd tracked down, alongside the other parts I wanted to throw together.. It's entirely possible it is the mobo that's causing this, I've looked and there are only drivers for XP and Vista 🙁

you are probably right that the hardware isn't itself incompatible, if its 2006 I'd imagine it should be ok but the lack of win98 drivers for the mb are a bit of a worry!

hopefully it works now, otherwise it could hard to track down without being able to swap out the mb to test that. To be honest I only put win98 on machines of around 200-1000mhz era, so haven't tried on later hardware

Run memtest86 there are bootable floppys for it. Report back. Sounds like defective ram.