I know this isn't a great answer, but it should get you started.
Go to the main lens, select applications, type in "hardware" or "device". There should still be a "device manager" syle application. See if your mouse shows up there and is enabled. You could also search for "mouse". The application that allows you to adjust the mouse settings might also allow you to select which mouse you use and/or enable/disable them.
Sorry this isn't better but I'm answering from my phone and not in front of my PC. Hopefully someone can improve this, or I can get back on later and improve it.
Update/Facepalm Moment: One thing I forgot to mention is that PS/2 Mice & keyboards generally have to be plugged in prior to booting the PC. If you plug it in after the boot process has started it will often not be recognized. You may already be aware of this, but I thought it might be worth a mention. I'm assuming you probably tried rebooting the offending machine a couple times?
You can find additional troubleshooting help here:
Sorry to hear you had to come to the point of a reinstall.