Problems are filling up the forums with pleas for help "my keyboard displays the wrong key", or "typing J, K, and L displays the wrong keys". On a laptop it's very easy to hit the Num Lock key by mistake and you can waste a lot of time checking keyboard settings, buying a new keyboards or even repair shops. Small keyboards have a Function key that is held down while pressing the Num Lock key to toggle some letters on your keyboard into a keypad for 0-9 (you'll see the numbers in another colour by these keys. On some keyboards you have to hold down the ALT key while pressing the Num Lock. Larger keyboards have a Num Lock key you just press to toggle it on - very easy to do by accident. Since most people use only the numbers across the top, it's a shame the system doesn't just allow you to disable this function.
Any easy way to prevent setting any Lock key by mistake is to use Microsoft Windows Accessibility settings to "beep" whenever you hit one. Go to the Control Panel (Start > Run > type "Control Panel") and find Ease of Access, then Ease of Access Center, then Make the keyboard easier to use (last item). Check the box for Toggle Keys. Click OK. Now when you hit the keys for Caps Lock, Num Lock, or Scroll Lock, you will hear a high tone (on), when you hit it again, you will hear a low tone (off). No more surprises when you are typing.
Another solution may be to turn off all Hot Keys that change your keyboard. Most computers have multiple language keyboards available. Go to Control Panel , then Regional and Language. then Keyboards and Languages tab, click Change Keyboards then hit the Advanced Key Settings tab. If any hot keys are set, change it to something you will never hit by accident, or even change it to "not assigned".
Hope these hints help someone. Sadly, I still have an intermittent problem on my laptop keyboard/external keyboard. Only some of my keys lose their mapping on some programs - I type " and get ` or / will displays é. Restarting (Firefox, Thunderbird, Notetab Pro) solves it. If anyone knows what causes this one, I'd be happy to hear from you!