So, I'm having some really weird trouble with my Unisys 486DX2/66 machine. It's a late PCI model with an intel chipset. I've had it for a few weeks, and I had it running Windows 95 stably and not really ever crashing. Then it started crashing, and eventually it got to where it would lock up after a few minutes just using DOS. After that, it started intermittently posting and locking up while loading DOS. Then not posting at all, and not showing output on a POST card. All within the span of a day, went from stable to not posting. I figured I just had a bad power supply.

I got and installed a old but unused ATX 1.0 Seasonic power supply with an adapter, and all was well for a few hours. I ran two cycles of Memtest 86 with no issues and checked the basic hardware with Amidiag. It was fine until I tried to copy over the C drive partition with Ghost and a laplink cable, locked up twice in a row. I tried to Laplink over the Ghost image file in DOS, but that crashed three times in a row after about twenty minutes or so. After the third Laplink try, it wouldn't post when I turned it off and back on again. It's now erratic, sometimes posting and sometimes not, seems to be getting worse, first stopped booting off a floppy, now crashes early in the POST. I was finding pulling the CMOS battery and waiting a few minutes would get it to post again if it wouldn't otherwise. The post card shows the machine stopping at various points in the boot, but often around the point where it accesses the floppy controller. I've seen it occasionally state that the CMOS battery is dead -- it's new and measures at 3.1 volts on my multimeter.

I have the machine down to just the one, original 500MB hard disk. I've removed the cache, the second RAM module, and all expansion cards. I've tried turning everything off in the BIOS, including shadowing, the floppy controller, the cache, APM, .etc. Makes no difference.

Any ideas? Is this really just two bad power supplies in a row?