So I've had this motherboard installed in a once Zeos 486/33 case and it has been working great for years. It was packed away for a few years and I just go around to cleaning it up and putting it back in service as a retro gaming machine. Everything is working great, but for one thing. The PS/2 mouse is having major issues. When the machine boots up, sometimes it can't find the mouse. When it does, it works fine for a moment and then jumps around erratically and clicking on anything in its path. At first I thought it was Windows 98, but it does the same thing when in BIOS. The mouse port is a header on the board and it uses the original backplate from Supermicro. For testing I purchased a new cable and plate, but it does the exact same.

Now I did also run into a problem with the keyboard as it wouldn't boot with it connected. I tracked that down to the resistor fuse and replaced it. The keyboard works perfectly again, but the hopes I had that it would fix the mouse were quickly doused as it didn't help.

Any clues on what might be going wrong? I've tried 3 different mice, so I know it's not the mouse. At the moment I'm using the mouse on a com port, but I want it back on the PS/2 port so I can use a KVM.

Thanks for any and all help.