I can only imagine a wrong usb controller driver would have that effect, but a PS/2 connection should not be affected.
If there is one, it doesn't hurt to try.
Safest way is to boot in safe mode and uninstall all the usb controllers and devices.
Upon reboot in windows, everything will reinstall with default windows drivers and all should work well.
Try it WarNoob14.
gigabyte X58A-UD3R rev.2, core i7 975 3.9ghz (stock voltage), windows 8.1 64-bit, corsair 12gb DDR3 1600mhz 7-7-7-20 RAM, xfx HD 5970 + gigabyte HD 5970 (stock clocks), coolermaster ultimate 900w PSU.
amd catalyst 14.7 RC3 aug12