Try booting without the mouse, clear CMOS settings, set CMOS settings to setup default, reboot.

Btw, I have that same AT case as you, except I do not have the numerical LCD speed display.

feipoa wrote:

Try booting without the mouse, clear CMOS settings, set CMOS settings to setup default, reboot.

Btw, I have that same AT case as you, except I do not have the numerical LCD speed display.

I don't even have a CMOS battery right now, so I guess the settings reset every time I reboot.

Do you know the model of that AT case, BTW?

Nothing seemed to work, so I tried reinstalling Win98SE. The problem is still there.

Also I tried booting without a mouse. The keyboard works, but the system reacts to the key strokes really slow and somewhat erraticaly. Also, the pu-pu-pu-pu stuttering sound is still there. Also, the mouse didn't work when I tried rebooting again.

Did you try a different keyboard? I've seen some 486 boards work with some keyboards and not others, even for the same model of motherboard.

I don't know the brand of the case either.

feipoa wrote:

Did you try a different keyboard? I've seen some 486 boards work with some keyboards and not others, even for the same model of motherboard.

I don't know the brand of the case either.

No, I don't have other PS/2 devices, and the machine does not have USB ports. But like I said, the keyboard and mouse stopped working only after I added the new hardware — everything was fine until then.

whenever i run into issues like this u have to peel stuff off the machine to avoid resource conflicts and add em back 1 at a tme

i had similar problems with a 3com card earlier this year.. actually two of them..
is it similar to the 3Com 3C509C-TX??
if so take it outttt and watch your problems disappear
i had really screwey things happen with those cards i had two and i kept getting confused as to which was good + which was bad. becuase they kept giving different results!!!! it might have something to do with pci spec? ie: pci spec 2.0 vs 2.1?

https://en.wikipedia.org/wiki/Conventional_PCI
check this chart for the times of pci spec revisions

pci 2.1 was around 1995.. maybe your board is 2.1 and the 3com card is 2.0 only
i had a similar nightmare with a powercolor ati radeon card

actually wait i think theres a .exe or .com app for configuring the 3com and you HAVE TO RUN IT

which motherboard do u have?
i would start over and check everythng in the manual for the board from scratch
including jumper settings
and keep the 3com card unplugged for a bit till things stabilize

HOLY $#@! SHIT (not sure if you can swear here, but I'd really like to)

Well, I just went to BIOS and checked the PCI/IRQ settings. Set "PNP OS" to yes (since I run Win 98) and set "Resources controlled by" to auto. Rebooted and everything works now. The keyboard, the mouse. Even the clicking sound stopped. I have no idea why those settings changed before, but I just wasted a couple of hours because of that.

The funny thing is, I did that for no reason, pure random luck. Control panel showed no resources conflict.

Normally I leave PNP OS set to "no" and Resourches controlled by "auto". Soundes like some of your manual resource settings were overriding the settings, e.g. IRQ, for the mouse/keyboard.

congrats:)