I unscrewed and put my keyboard to pieces and didn't notice anything unusual. But after reassembling it, it worked !
This already happened to me. I don't remember if I solved it or waited until I formated my computer, but I know the button is not damaged.
I tried on the notepad, the calculator, any text editor and any other program, but the numpad "." button does nothing (num lock being activated or not).
I tried uninstalling the driver from the device manager, but as soon as I reconnect the keyboard, the driver installs back instantly, as if it wasn't really uninstalled.
Any advice ?
I'm on windows 7 64 bits and my keyboard is a microsoft comfort curve keyboard 2000.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic