|Typing in all capital letters in a post on the internet is considered to be the same as if you were SHOUTING, and to be very rude !|
"Somewhere on your keyboard there should be a number lock key. It will be labelled "num lck" or something very similar. The next time this happens, press the key and see if that changes the behavior"
Look at the keys you're pressing you're getting the wrong character for - is the number you're getting and the letter you want on the same key and they're different colors? If so, there is some key or key combo you must press to toggle the characters to the other colored ones. You MAY need to press two keys to toggle Num Lock on / off on a laptop - e.g. on a Acer laptop I have here, Fn and F11.
Make sure that are no keyboard keys stuck in the down position.
See the Owner's or User's manual for the model - some laptops have key combos that can toggle an alternate character set on / off.
Other than the above, I know of no situation where you get numbers for many letter keys or visa versa.
You can get a different character than what the key has on it in some situations, if settings are screwed up in Windows, but I have not heard of any situation like that, that would result in what you're describing.
If you dropped the laptop, or if you have spilled liquid on the keyboard or anywhere on the laptop, all sorts of strange symptoms are possible - in that case, the keyboard, and/or something else, is probably damaged and you need to replace it.
A USB keyboard plugged directly into a USB port built into the laptop should work fine. If it doesn't, some setting in Windows is screwed up, or your mboard is damaged.