@omap621, These type of cases are not hardware problems; they're software. The thing is, electrically a lowercase 'p' is the same signal as an uppercase 'P'; the case is determined by the keyboard device driver; that 'p' signal is modified depending on the state of the Shift or Caps Lock buttons.
So what you're looking for is a program that has changed the keyboard bindings. I'd try restarting in safe mode and see if the problem goes away, or enter the BIOS setup screen and test there. If the key works then, you'll have to get into the Task Manager and start killing programs until you find the one that's rebinding your key.