Are you using a notebook computer?
Notebook computers often have a limited keyboard- i.e., they do not have the little numeral section to the right, so if you press certain key combinations simultaneously, it can change the way certain keys work. For example, on my Dell notebook, in the lower left corner by the "Ctrl" key is a key with "Fn" printed in blue (Fn stands for Function, I believe). If I hit the "Fn" key in combination with certain other keys with blue print, it changes my keyboard over into a different function. To change back, you just need to figure out what combination you struck and repeat the act to return to normal function. I hope this is the case and that all this makes sense. Then again, it could be some virus or something like that, as Charlie99 suggested.
Good luck.