Something I have learned the hard way, over the years: one needs to ALWAYS have a wired keyboard handy.
You need to beg, borrow or steal one to access your computer. I'm not familiar with the driver for this keyboard, but I'm assuming there is a Preferences pane you need to check for it. Or maybe not. Either way, you might need to check if you need to install a new driver, or perhaps uninstall and install again the same one.
And, regardless, you need to keep an El Cheapo wired keyboard for emergencies like this.
Well, the MS website only shows updates of the driver up to Lion:
So there is a possibility that the upgrade completely broke the driver. and that you'll have to wait for a new one.
Again, you'll need that Mr. Cheapov wired keyboard, one way or the other...