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.
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amd catalyst 14.12 Omega Driver