Try any of these methods. I wouldn't suggest rebuilding as I'm not sure what good that will do with toggle keys, sticky keys, and hot keys... so let's start small and see if this works.

Here's something funny. Try holding down both shift keys at the same time, or just using the right shift key. and you've unchecked use shortcut under the filter keys option? If that doesn't work then another method to try may be system restore, or a virus and trojan scan.