I've been doing some experimenting which may do something for you if you don't have a PS/2 mouse.
I created a restore point and uninstalled my PS/2 Compatible mouse driver and after the reboot it was still there in Device Manager but with a yellow alert next to and no amount of Scan for hardware changes would reinstate it and when I did the Update driver software bit - it returned that I had the latest drivers.
A Google found
http://www.driverscape.com/download/microsoft-ps-2-mouseThe Mouse Driver Installer just gives you an Updater program which is a paid for job for it to update drivers, but the actual Driver download below that gave me a Synaptics Touchpad driver for my Toshiba laptop (10 mins to download when I clicked on Run)
After I ran the Set up and checked Device Manager after the reboot, the yellow alerted PS/2 Compatible mouse driver had been replaced with Synaptics PS/2 Port Touchpad.
Not exactly what I was expecting, but as I don't have a PS/2 mouse to try the reinstate, that seems the best it could do for my laptop but it may give something more apt for you as it recognizes your OS.
It's possible that your screwed PS/2 is the cause of all of your problems so getting any update to get rid of the yellow alert may sort your Boot problems.