My cat sat on my laptop and now if I type either L or P, it inputs 3 or * instead. The rest of my keyboard still works correctly. The problem is bad enough that I had to use the touch screen of my computer to type this in.
How can I restore the correct working behaviour of my keyboard?
You need to turn off Num Lock and it will work as expected again.
On my ASUS laptop the key combination is Fn + Insert.
Your keyboard is now set to be the numeric pad; this is accomplished with a Fn key press plus another key, which varies by manufacturer. The proof to this is to check the other keys: O, I, K, M, N, J.
If they also produce numeric keypad numbers, then, you need to press the Fn key combination again to toggle off the keyboard numeric keypad.
If they do NOT produce the keypad numbers, then your keyboard is broken. Use a paperclip and scoop out that dingleberry from underneath the L and P keys, and banish the cat from future use of your laptop.
On Windows, Alt + Shift toggles key mapping on and off. Your cat could have hit those keys when using your keyboard as its personal cushion.
Press Alt + Shift again to restore standard keyboard behavior.
