OK, I know this topic has refused to die, but I gotta jump in. My computer was driving me crazy - sometimes typing backwards, sometimes refusing to scroll down, sometimes activating just the upper left icon on my desktop regardless of which one I actually clicked on. Neat trick. These were intermittent problems, and occasionally showed up at the same time. Generally rebooting sorted the issue out, but having to play with it was getting old.
I finally found that my 'Scroll Lock' key was sticking, although it wasn't apparent. That same key shares functionality with the 'Insert' key, and between the two, they were driving me crazy. Bottom line - clean the 'Scroll Lock' key, and perhaps the 'Insert' key as well.
Go nuts, clean the whole keyboard. Hope this helps.