This issue started after my cat walked all over the keyboard...

Whenever I press the "zero" key, the screen goes black and I'm taken to the lock/switch user screen. The other functions of the key work fine - it can produce ) and / like usual. Numlock is off, and as far as I know, my computer doesn't have Function Lock. If I log out of my user account and sign in as a guest, the "zero" works again, but if I create a new user profile, it doesn't work. I get the same issue when I hit "zero" using the on-screen keyboard. My keyboard layout is set to US English. I've uninstalled and reinstalled the ATK package, and updated my keyboard drivers. I have an ASUS U43JC-X1 laptop running Windows 7, and I haven't installed any new programs lately.