Hi
I'm going to suggest my standard solution for any hardware that doesn't work in Windows. LOL
Go to device manager, open Human Interface Devices, uninstall everything that says Keyboard, and then reboot your computer.
This will force Windows to try and redetect and reinstall the keyboard to the normal settings and drivers.
This is a pretty basic Windows function it's weird for it to not work, but my keyboard does stop working from time to time, but unplugging it and plugging it back in always fixes it.
You could also try plugging it into a different USB port, and see if that makes any difference if you haven't already tried that.
Mike