He has Windows98 SE. The pc has no problems with current serial mouse - it is the mouse itself that is not functioning well (eg. you have to press the buttons really hard and repeatedly for it to work - and it used to work fine before. I also cleaned it and checked the settings..)
We want to hook up a ps2 mouse to this pc, but it only has a serial port and when I use the serial-to-ps2 adapter, the pc won't see the mouse. Without the mouse working, I can't check for the conflicts in device manager, and if I switch back to serial mouse, there are not conflicts then, naturally.