Left Click Not Working

Running Windows 7, Java fully updated. No texture packs or mods running. The left click (Button 1) is not working on either single player or multiplayer, regardless of survival or creative mode. I can't pick things up out of my inventory without right clicking, which divides things in half and places things one at a time, so picking up whole stacks is impossible.

I've tried uninstall/reinstall but it didn't work. This was not an issue before the 1.4.2 update.