I found an old Micron Pentium II motherboard with a PII-266, and tossing it on my workbench I couldn't get it to boot. It's got a Phoenix BIOS and it halts with a post code of 49.

On my workbench, I have a random Dell P2414H monitor with an integrated USB hub. My workbench keyboard and mouse plugs into the monitor, and then I have a USB upstream cable that I plug into various machines. I have used this setup for years, and never had a problem with any machine with USB ports using the attached keyboard and mouse.

Except this Micron board. If the USB cable to my monitor with integrated hub is plugged into either of the USB ports on this thing, it will not boot. No beeps, halts on post code 49.

If I remove the USB cable to my monitor, boots fine. It's got PS/2 ports, too, so I hooked up a PS/2 keyboard and slapped a hard drive on the thing, boots and runs just fine. I connected a random USB keyboard directly to the USB ports... boots and runs just fine.

But as soon as I connect the cable that runs to the Dell P2414H - nothing. Won't boot.

If the machine is booted and I connect the hub cable to the USB ports, the PS/2 keyboard will stop working. But a regular, directly connect USB keyboard, everything is fine - both keyboards work simultaneously.

What is happening here? Weird BIOS bug? Some incompatibility with the USB hub in the Dell monitor and my USB controller - which I think is chipset integrated on this motherboard?